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Document and Entity Information - USD ($)	12 Months Ended
Document and Entity Information - USD ($)	Dec. 31, 2018	Mar. 01, 2019	Jun. 29, 2018
Document And Entity Information [Abstract]
Entity Registrant Name	Aerpio Pharmaceuticals, Inc.
Entity Central Index Key	0001422142
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Document Type	10-K
Document Period End Date	Dec. 31, 2018
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	FY
Trading Symbol	ARPO
Entity Well-known Seasoned Issuer	No
Entity Filer Category	Accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	true
Entity Shell Company	false
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Public Float			$ 101,488,694
Entity Common Stock, Shares Outstanding		40,588,004

Consolidated Balance Sheets - USD ($)	Dec. 31, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 62,614,010	$ 20,264,109
Prepaid research and development contracts	754,392	313,140
Other current assets	615,681	322,221
Total current assets	63,984,083	20,899,470
Furniture and equipment, net	98,449	107,223
Deposits	40,960	20,960
Total assets	64,123,492	21,027,653
Current liabilities:
Accounts payable and accrued expenses	5,456,917	3,592,164
Total current liabilities	5,456,917	3,592,164
Commitments and contingencies (Note 11)
Stockholders’ equity:
Common stock, $0.0001 par value per share; 300,000,000 shares authorized and 40,588,004 and 27,070,038 shares issued and outstanding at December 31, 2018 and 2017, respectively.	4,059	2,707
Additional paid-in capital	177,621,807	125,995,438
Accumulated deficit	(118,959,291)	(108,562,656)
Total stockholders’ equity	58,666,575	17,435,489
Total liabilities and stockholders’ equity	$ 64,123,492	$ 21,027,653

Consolidated Statements of Operations and Comprehensive Loss - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Income Statement [Abstract]
License revenue, and other	$ 20,157,430
Type of Revenue [Extensible List]	arpo:LicenseRevenueAndOtherMember
Operating expenses
Research and development	$ 17,852,756	$ 12,147,132
General and administrative	13,485,918	9,241,411
Total operating expenses	31,338,674	21,388,543
Loss from operations	(11,181,244)	(21,388,543)
Grant income	6,394	93,719
Interest income (expense), net	778,215	(105,782)
Total other income (expense)	784,609	(12,063)
Net and comprehensive loss	(10,396,635)	(21,400,606)
Reconciliation of net loss attributable to common stockholders:
Net and comprehensive loss	(10,396,635)	(21,400,606)
Adjustment of redeemable convertible preferred stock to redemption value		(943,297)
Net loss attributable to common stockholders	$ (10,396,635)	$ (22,343,903)
Net loss per share attributable to common stockholders, basic and diluted	$ (0.31)	$ (1.03)
Weighted average number of common shares used in computing net loss per share attributable to common stockholders, basic and diluted	33,930,846	21,673,349

Consolidated Statements of Redeemable Convertible Preferred Stock and Stockholders' Equity (Deficit) - USD ($)	Total	Redeemable Convertible Preferred Stock [Member]	Common Stock [Member]	Additional Paid-In Capital [Member]	Accumulated Deficit [Member]
Redeemable convertible preferred stock, Balance at Dec. 31, 2016		$ 73,757,890
Redeemable convertible preferred stock, Balance, Shares at Dec. 31, 2016		14,015,016
Balance at Dec. 31, 2016	$ (86,218,629)		$ 124		$ (86,218,753)
Balance, Shares at Dec. 31, 2016			1,240,925
Redeemable convertible preferred stock, Adjustment of redeemable convertible preferred stock to redemption value		$ 943,297
Adjustment of redeemable convertible preferred stock to redemption value	(943,297)				(943,297)
Redeemable convertible preferred stock, Conversion of preferred stock		$ (74,701,187)
Redeemable convertible preferred stock, Conversion of preferred stock, Shares		(14,015,016)
Conversion of redeemable convertible preferred stock	74,701,187		$ 1,402	$ 74,699,785
Conversion of redeemable convertible preferred stock, Shares			14,015,016
Conversion of convertible notes and accrued interest	13,447,934		$ 274	13,447,660
Conversion of convertible notes and accrued interest, Shares			2,744,059
Share exchange in connection with Merger			$ 100	(100)
Share exchange in connection with Merger, Shares			1,000,000
Issuance of common stock,net of issuance costs	37,163,390		$ 805	37,162,585
Issuance of common stock, net of issuance costs, Shares			8,049,555
Issuance of common stock upon exercise of stock options	$ 36,101		$ 3	36,098
Issuance of common stock upon exercise of stock options, Shares	25,729		25,729
Forfeiture of restricted stock			$ (1)	1
Forfeiture of restricted stock, Shares			(5,246)
Share-based compensation expense	$ 649,409			649,409
Net and comprehensive loss	(21,400,606)				(21,400,606)
Balance at Dec. 31, 2017	17,435,489		$ 2,707	125,995,438	(108,562,656)
Balance, Shares at Dec. 31, 2017			27,070,038
Issuance of restricted stock			$ 6	(6)
Issuance of restricted stock, Shares			60,000
Issuance of common stock,net of issuance costs	48,119,027		$ 1,341	48,117,686
Issuance of common stock, net of issuance costs, Shares			13,408,200
Issuance of common stock upon exercise of stock options	$ 76,832		$ 5	76,827
Issuance of common stock upon exercise of stock options, Shares	52,099		52,099
Forfeiture of restricted stock, Shares			(2,333)
Share-based compensation expense	$ 3,431,862			3,431,862
Net and comprehensive loss	(10,396,635)				(10,396,635)
Balance at Dec. 31, 2018	$ 58,666,575		$ 4,059	$ 177,621,807	$ (118,959,291)
Balance, Shares at Dec. 31, 2018			40,588,004

Consolidated Statements of Cash Flows - USD ($)	12 Months Ended
Consolidated Statements of Cash Flows - USD ($)	Dec. 31, 2018	Dec. 31, 2017
Operating activities:
Net and comprehensive loss	$ (10,396,635)	$ (21,400,606)
Adjustments to reconcile net and comprehensive loss to net cash used in operating activities:
Depreciation	46,686	51,268
Stock-based compensation	3,431,862	649,409
Amortization of debt issuance costs		75,561
Interest expense related to convertible note conversion		204,929
Changes in operating assets and liabilities:
Prepaid research and development contracts	(441,252)	40,294
Other current assets	(293,460)	(109,026)
Deposits	(20,000)
Accounts payable and accrued expenses	1,864,753	1,604,636
Net cash used in operating activities	(5,808,046)	(18,883,535)
Investing activities:
Purchase of furniture and equipment	(37,912)	(8,896)
Proceeds from maturities of short-term investments		50,000
Net cash (used in) provided by investing activities	(37,912)	41,104
Financing activities:
Proceeds from exercise of stock options	76,832	36,100
Proceeds from issuances of convertible notes		297,354
Proceeds from sale of common stock	51,621,570	40,247,777
Cash paid in connection with the sale of common stock	(3,502,543)	(3,084,385)
Net cash provided by financing activities	48,195,859	37,496,846
Net increase in cash and cash equivalents	42,349,901	18,654,415
Cash and cash equivalents at beginning of year	20,264,109	1,609,694
Cash and cash equivalents, at end of year	$ 62,614,010	20,264,109
Non-cash financing activities
Conversion of redeemable convertible preferred stock into common stock		74,701,187
Conversion of convertible notes and accrued interest into common stock		13,447,934
Accretion of redeemable convertible preferred stock to redemption value		$ 943,297

Nature of Organization and Operations

12 Months Ended

Dec. 31, 2018

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Nature of Organization and Operations

1. Nature of Organization and Operations

Aerpio Pharmaceuticals, Inc. (the “Company”) incorporated as Zeta Acquisition Corp. II (“Zeta”) in the State of Delaware on November 16, 2007. Prior to the Merger, (as defined below), Zeta was a “shell company” (as defined in Rule 12b-2 of the Securities Exchange Act of 1934, as amended).

On March 3, 2017, the Company’s Board of Directors, and on March 10, 2017, the Company’s pre-Merger (as defined below) stockholders, approved an amended and restated certificate of incorporation, which, among other things, increased authorized capital stock from 100,000,000 shares of common stock, par value $0.0001 per share, and 10,000,000 shares of preferred stock, par value $0.0001 per share, to 300,000,000 shares of common stock, par value $0.0001 per share, and 10,000,000 shares of preferred stock, par value $0.0001 per share.

On March 15, 2017, Zeta changed its name to Aerpio Pharmaceuticals, Inc. and its wholly-owned subsidiary, Aerpio Acquisition Corp., a corporation formed in the State of Delaware on March 3, 2017, merged with and into Aerpio Therapeutics, Inc., (“Aerpio”), (the “Merger”), a corporation incorporated on November 17, 2011 in the State of Delaware. Pursuant to the Merger, Aerpio remained as the surviving corporation and became the Company’s wholly-owned subsidiary.

At the effective time of the Merger, the shares of the Aerpio’s (i) common stock issued and outstanding immediately prior to the closing of the Merger (including restricted common stock, whether vested or unvested, issued under the Aerpio’s 2011 Equity Incentive Plan), and (ii) redeemable convertible preferred stock issued and outstanding immediately prior to the closing of the Merger, were converted into shares of the Company’s common stock. In addition, immediately prior to the Merger, the outstanding amounts under certain senior secured convertible notes issued by Aerpio to its pre-Merger noteholders were converted into shares of Aerpio’s preferred stock, which were then converted to shares of Aerpio’s common stock and subsequently were converted into shares of the Company’s common stock, together with the other shares of Aerpio’s common stock described above. In addition, pursuant to the Merger Agreement options to purchase shares of Aerpio’s common stock issued and outstanding immediately prior to the closing of the Merger were assumed and converted into options to purchase shares of the Company’s common stock. All the outstanding capital stock of Aerpio was converted into shares of the Company’s common stock on a 2.3336572:1 basis.

As a result of the Merger, the Company acquired the business of Aerpio and has continued the existing business operations of Aerpio as a public reporting company under the name Aerpio Pharmaceuticals, Inc. Immediately after the Merger, on March 15, 2017, Aerpio converted into a Delaware limited liability company (the “Conversion”).

Immediately following the Conversion, the pre-Merger stockholders of Zeta surrendered for cancellation 4,000,000 of the 5,000,000 shares of the outstanding common stock of Zeta, (the “Share Cancellation”). Following the Share Cancellation, on March 15, 2017, the Company closed a private placement offering (the “2017 Offering”) of 8,049,555 shares of the Company’s common stock, at a purchase price of $5.00 per share, for net proceeds of $37.2 million and the issuance of warrants with a term of three years, to purchase 317,562 shares of the Company’s common stock at an exercise price of $5.00 per share.

The Merger was treated as a recapitalization and reverse acquisition for financial reporting purposes. The Company is the legal acquirer of Aerpio in the transaction. However, Aerpio is considered the acquiring company for accounting purposes since (i) former Aerpio stockholders owned in excess of 50% of the combined enterprise on a fully diluted basis immediately following the Merger and 2017 Offering, and (ii) all members of the Company’s executive management and Board of Directors were from Aerpio. In accordance with “reverse merger” or “reverse acquisition” accounting treatment, the consolidated financial statements for the years ended December 31, 2018 and 2017 include the accounts of the Company and its wholly owned subsidiary, Aerpio Therapeutics, LLC.

On June 28, 2018, the Company closed an underwritten public offering for the sale of 11,688,000 shares of its common stock, and subsequently on July 2, 2018, the Company closed on the sale of an additional 1,720,200 shares of its common stock, pursuant to the underwriters’ partial exercise of their option to purchase additional shares of common stock (the “2018 Offering”). In the aggregate, the Company received net proceeds of $48.1 million from the 2018 Offering after a deduction of $3.5 million related to underwriting discounts and commissions and offering expenses paid in conjunction with the 2018 Offering.

The Company is a biopharmaceutical company focused on advancing first-in-class treatments for ocular disease. The Company’s lead product candidate, AKB-9778, a small molecule activator of the Tie2 pathway, is being developed for the treatment of non-proliferative diabetic retinopathy (“NPDR”). Tie2 signaling is essential for regulating blood vessel development and the stability of mature vessels. The Company has completed a Phase 2a clinical trial in diabetic macular edema (“DME”), a swelling of the retina that is a common cause of vision loss in patients with DR and during the second quarter of 2017, initiated a double-blind Phase 2b clinical trial in patients with DR who have not developed more serious complications such as DME or proliferative diabetic retinopathy.

In addition, the Company has a pipeline program, ARP-1536, a humanized monoclonal antibody drug candidate for ocular disease. Humanized antibodies are antibodies from non-human species whose protein sequences have been modified to increase their similarity to antibodies produced naturally in humans. The Company is currently in preclinical development for ARP-1536.

The Company’s operations to date have been limited to organizing and staffing the Company, business planning, raising capital, acquiring and developing its technology, identifying potential product candidates and undertaking preclinical and clinical studies. The Company’s revenue has been primarily limited to license revenue from Gossamer Bio. Inc., (“Gossamer”) pursuant to a license agreement (“Gossamer License”). Future revenue is dependent on the terms of the Gossamer License. The Company’s product candidates are subject to long development cycles and there is no assurance the Company will be able to successfully develop, obtain regulatory approval for, or market its product candidates.

The Company is subject to a number of risks similar to other life science companies in the current stage of its life cycle including, but not limited to, the need to obtain adequate additional funding, possible failure of preclinical testing or clinical trials, the need to obtain marketing approval for its product candidates, competitors developing new technological innovations, the need to successfully commercialize and gain market acceptance of any of the Company’s products that are approved, and protection of proprietary technology. If the Company does not successfully commercialize any of its products or mitigate any of these other risks, it will be unable to generate revenue or achieve profitability.

The Company incurred losses from operations and had a negative cash flows from operating activities for the years ended December 31, 2018 and 2017 (and since inception). The Company’s current operating plan indicates that it will continue to incur losses from operations and generate negative cash flows from operating activities given ongoing expenditures related to the completion of its ongoing clinical trials and the Company’s lack of product revenue generating activities. However, the Company believes it has the ability to control its current operating plan and that existing cash and cash equivalents of approximately $62.6 million at December 31, 2018 will be sufficient to allow the Company to fund its current operating plan into at least the second quarter of 2020, and as a result, through at least twelve months from the filing of the Company’s 2018 Annual Report on Form 10-K.

There can be no assurance, however, that the current operating plan will be achieved in the time frame anticipated by the Company, or that its cash resources will fund the Company’s operating plan for the period anticipated by the Company or that additional funding will be available on terms acceptable to the Company, or at all. The Company will need to raise additional funds in order to further advance its clinical research programs, commence additional clinical trials, and operate its business and meet its obligations as they come due. The Company is pursuing financing alternatives, which include permanent equity financing, business development arrangements, and licensing arrangements. However, financing may not be available to the Company in the necessary time frame, in amounts that the Company requires, on terms that are acceptable to the Company, or at all. If the Company raises additional funds through collaboration, licensing or other similar arrangements, it may be necessary to relinquish valuable rights to its potential products or proprietary technologies or grant licenses on terms that are not favorable to the Company. If the Company is unable to raise the necessary funds when needed or reduce spending on currently planned activities, it may not be able to continue the development of its product candidates or the Company could be required to delay, scale back, or eliminate some or all of its development programs and other operations and will materially harm its business, financial position and results of operations.

Summary of Significant Accounting Policies

12 Months Ended

Dec. 31, 2018

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

2. Summary of Significant Accounting Policies

Basis of Presentation

The consolidated financial statements have been prepared in conformity with U.S. generally accepted accounting principles (U.S. GAAP). Any reference in these notes to applicable guidance is meant to refer to the authoritative U.S. GAAP as found in the Accounting Standards Codification (ASC) and Accounting Standards Update (ASU) of the Financial Accounting Standards Board (FASB).

The Company’s consolidated financial statements are prepared in accordance with U.S. GAAP and stated in U.S. dollars.

Segment Information

Operating segments are defined as components of an enterprise about which separate discrete information is available for evaluation by the chief operating decision maker, or decision-making group, in deciding how to allocate resources and in assessing performance. The Company views its operations and manages its business in one operating segment, which is the business of developing and commercializing proprietary therapeutics. All the assets and operations of the Company are located in the U.S.

Use of Estimates

The preparation of consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the consolidated financial statements and the reported amounts of revenue and expenses during the reporting period. Actual results may differ from those estimates. Management considers many factors in selecting appropriate financial accounting policies and controls, and in developing the estimates and assumptions that are used in the preparation of these consolidated financial statements. Management must apply significant judgment in this process. In addition, other factors may affect estimates, including: expected business and operational changes, sensitivity and volatility associated with the assumptions used in developing estimates, and whether historical trends are expected to be representative of future trends. The estimation process often may yield a range of potentially reasonable estimates of the ultimate future outcomes, and management must select an amount that falls within that range of reasonable estimates. Estimates are used in the following areas, among others: prepaid and accrued research and development expense, stock-based compensation expense, revenue recognition and income taxes.

Cash and Cash Equivalents

Cash and cash equivalents consist of all cash on hand, certificates of deposits, and funds invested in available for sale securities with original maturities of three months or less at the time of purchase. At December 31, 2018 and 2017, the Company’s cash equivalents are primarily in money market funds. The Company has maintained balances with its banks in excess of federally insured limits.

Revenue Recognition

At the inception of an arrangement, the Company evaluates if a counterparty to a contract is a customer, if the arrangement is within the scope of revenue from contracts with customers guidance and the term of the contract. The Company recognizes revenue when its customer obtains control of promised goods or services in a contract for an amount that reflects the consideration the Company expects to receive in exchange for those goods or services. For contracts with customers, the Company applies the following five-step model in order to determine this amount: (i) identification of the promised goods or services in the contract; (ii) determination of whether the promised goods or services are performance obligations, including whether they are distinct in the context of the contract; (iii) measurement of the transaction price, including the constraint on variable consideration; (iv) allocation of the transaction price to the performance obligations; and (v) recognition of revenue when (or as) the Company satisfies each performance obligation. The Company only applies the five-step model to contracts when it is probable that the entity will collect the consideration it is entitled to in exchange for the goods or services it transfers to the customer. As part of the accounting for contracts with customers, the Company must develop assumptions that require judgment to determine the standalone selling price of each performance obligation identified in the contract. The Company then allocates the total transaction price to each performance obligation based on the estimated standalone selling prices of each performance obligation. The Company recognizes the amount of the transaction price as revenue that is allocated to the respective performance obligation when the performance obligation is satisfied or as it is satisfied.

The Company enters into collaboration arrangements, under which it licenses certain rights to its intellectual property to third parties. The terms of these agreements may include payment to the Company of one or more of the following: nonrefundable upfront license fees; development, sale and commercial milestone payments and royalties on net sales of licensed products. Each of these types of payments are classified as license revenue except for revenue from royalties on net sales of licensed products, which are classified as royalty revenue.

For each collaboration agreement that results in revenues, the Company identifies all material promised goods and services, which may include a license to intellectual property, research and development activities and/or transition activities. Promised goods or services are considered to be separate performance obligations if they are distinct. In order to determine the transaction price to be allocated to each performance obligation, in addition to any upfront payment, the Company estimates the amount of variable consideration at the outset of the contract either utilizing the expected value or most likely amount method, depending on the facts and circumstances relative to the contract. The Company constrains (reduces) the estimates of variable consideration such that it is probable that a significant reversal of previously recognized revenue will not occur throughout the life of the contract. When determining if variable consideration should be constrained, management considers whether there are factors outside the Company’s control that could result in a significant reversal of revenue. In making these assessments, the Company considers the likelihood and magnitude of a potential reversal of revenue. These estimates are re-assessed each reporting period as required.

Once the estimated transaction price is established, amounts are allocated to the performance obligations that have been identified. The transaction price is generally allocated to each separate performance obligation on a relative standalone selling price basis. The Company must develop assumptions that require judgment to determine the standalone selling price (SSP) in order to account for these agreements. To determine the standalone selling price the Company’s assumptions may include (i) assumptions regarding the probability of obtaining marketing approval for the drug candidate; (ii) estimates regarding the timing of and the expected costs to develop and commercialize the drug candidate; (iii) estimates of future cash flows from potential product sales with respect to the drug candidate; and (iv) appropriate discount and tax rates. Standalone selling prices used to perform the initial allocation are not updated after contract inception. The Company does not include a financing component to its estimated transaction price at contract inception unless it estimates that certain performance obligations will not be satisfied within one year.

Upfront License Fees

If a license to the Company’s intellectual property is determined to be distinct from the other performance obligations identified in the arrangement, the Company recognizes revenues from nonrefundable, upfront license fees based on the relative value prescribed to the license compared to the total value of the arrangement. The revenue is recognized when the license is transferred to the collaborator and the collaborator is able to use and benefit from the license. For licenses that are not distinct from other obligations identified in the arrangement, the Company utilizes judgment to assess the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time. If the combined performance obligation is satisfied over time, the Company applies an appropriate method of measuring progress for purposes of recognizing revenue from nonrefundable, upfront license fees. The Company evaluates the measure of progress each reporting period and, if necessary, adjusts the measure of performance and related revenue recognition.

Development Milestone Payments

Depending on facts and circumstances, the Company may conclude it is appropriate to include the milestone in the estimated transaction price using the most likely amount method or it is appropriate to fully constrain the milestone. A milestone payment is included in the transaction price in the reporting period the Company concludes that it is probable that recording revenue in the period will not result in a significant reversal in amounts recognized in future periods. The Company may record revenues from certain milestones in a reporting period before the milestone is achieved if the Company concludes that achievement of the milestone is probable and that recognition of revenue related to the milestone will not result in a significant reversal in amounts recognized in future periods. The Company records a corresponding contract asset when this conclusion is reached. Milestone payments that have not been included in the transaction price to date are fully constrained. These milestones remain fully constrained until the Company concludes that achievement of the milestone is probable and recognition of revenue related to the milestone will not result in a significant reversal in amounts recognized in future periods. The Company re-evaluates the probability of achievement of such development milestones and any related constraint each reporting period. The Company adjusts its estimate of the overall transaction price, including the amount of collaborative revenue that it has recorded, if necessary.

Sales-based Milestone and Royalty Payments

The Company’s collaborators may be required to pay the Company sales-based milestone payments or royalties on future sales of commercial products. The Company recognizes revenues related to sales-based milestone and royalty payments upon the later to occur of (i) achievement of the collaborator’s underlying sales or (ii) satisfaction of any performance obligation(s) related to these sales, in each case assuming the license to the Company’s intellectual property is deemed to be the predominant item to which the sales-based milestones and/or royalties relate.

Grant Income

Grant income is recognized as earned based on contract work performed.

Research and Development

Research and development costs are expensed as incurred. Research and development expense consists of (i) employee-related expenses, including salaries, benefits, travel and stock-based compensation expense; (ii) external research and development expenses incurred under arrangements with third parties, such as contract research organizations and consultants; (iii) the cost of acquiring, developing and manufacturing clinical study materials; and (iv) costs associated with preclinical activities and regulatory operations.

The Company enters into consulting, research, and other agreements with commercial firms, researchers, universities and others for the provision of goods and services. Under such agreements, the Company may pay for services on a monthly, quarterly, project or other basis. Such arrangements are generally cancellable upon reasonable notice and payment of costs incurred. Costs are considered incurred based on an evaluation of the progress to completion of specific tasks under each contract using information and data provided to the Company by its clinical sites and vendors. These costs consist of direct and indirect costs associated with specific projects, as well as fees paid to various entities that perform certain research on behalf of the Company.

Patents

Costs incurred in connection with the application for and issuances of patents are expensed as incurred.

Income Taxes

Income taxes are recorded in accordance with ASC Topic 740, Income Taxes, or ASC 740, which provides for deferred taxes using an asset and liability approach. The Company recognizes deferred tax assets and liabilities for the expected future tax consequences of events that have been included in the consolidated financial statements or tax returns. Deferred tax assets and liabilities are determined based on the difference between the consolidated financial statement and tax bases of assets and liabilities and for loss and credit carryforwards using enacted tax rates anticipated to be in effect for the year in which the differences are expected to reverse. Valuation allowances are provided, if, based upon the weight of available evidence, it is more likely than not that some or all of the deferred tax assets will not be realized.

The Company accounts for uncertain tax positions in accordance with the provisions of ASC 740. When uncertain tax positions exist, the Company recognizes the tax benefit of tax positions to the extent that the benefit will more likely than not be realized. The determination as to whether the tax benefit will more likely than not be realized is based upon the technical merits of the tax position, as well as consideration of the available facts and circumstances. As of December 31, 2018 and 2017, the Company does not have any uncertain tax positions. The Company recognizes interest and penalties related to uncertain tax positions, if any exist, in income tax expense.

Net Loss per Share Attributable to Common Stockholders

The Company’s basic net loss per share attributable to common stockholders is calculated by dividing the net loss attributable to common stockholders by the weighted average number of shares of common stock outstanding for the period. The diluted net loss per share attributable to common stockholders is computed by adjusting the weighted average shares outstanding for the dilutive effect of common stock equivalents outstanding for the period, determined using the treasury stock method.

Stock-Based Compensation

The Company accounts for its stock-based compensation awards in accordance with ASC Topic 718, Compensation – Stock Compensation, or ASC 718. ASC 718 requires all stock-based payments to employees, including grants of employee stock options and restricted stock, to be recognized in the consolidated statements of operations and comprehensive loss based on their fair values. All the Company’s stock-based awards are subject only to service-based vesting conditions. The Company estimates the fair value of its stock-based awards using the Black-Scholes option pricing model, which requires the input of assumptions, including (a) the expected stock price volatility, (b) the calculation of expected term of the award, (c) the risk-free interest rate and (d) expected dividends. The fair value of restricted stock awards is determined based on the Company’s estimated common stock value.

Due to the historical lack of a public market for the trading of the Company’s common stock and a lack of company-specific historical and implied volatility data, the Company has based its estimate of expected volatility on the historical volatility of a group of similar companies that are publicly traded. The computation of expected volatility is based on the historical volatility of a representative group of companies with similar characteristics to the Company, including stage of product development and life science industry focus. The Company believes the group selected has sufficient similar economic and industry characteristics and includes companies that are most representative of the Company.

The Company uses the simplified method as prescribed by the SEC Staff Accounting Bulletin No. 107, Share-Based Payment, to calculate the expected term, as it does not have sufficient historical exercise data to provide a reasonable basis upon which to estimate the expected term for options granted to employees, and utilizes the contractual term for options granted to non-employees. The expected term is applied to the stock option grant group as a whole, as the Company does not expect substantially different exercise or post-vesting termination behavior among its employee population. The risk-free interest rate is based on a treasury instrument whose term is consistent with the expected life of the stock options.

Compensation expense related to awards to employees is calculated on a straight-line basis by recognizing the grant date fair value over the associated service period of the award, which is generally the vesting term.

Fair Value of Financial Instruments

The Company’s financial instruments consist of cash and cash equivalents, accounts payable and accrued expenses. The Company values cash equivalents using quoted market prices. The fair value of accounts payable and accrued expenses approximates its carrying value because of its short-term nature.

The Company is required to disclose information on all assets and liabilities reported at fair value that enables an assessment of the inputs used in determining the reported fair values. ASC Topic 820, Fair Value Measurements and Disclosures (ASC 820), establishes a hierarchy of inputs used in measuring fair value that maximizes the use of observable inputs and minimizes the use of unobservable inputs by requiring that the observable inputs be used when available.

Observable inputs are inputs that market participants would use in pricing the asset or liability based on market data obtained from sources independent of the Company. Unobservable inputs are inputs that reflect the Company’s assumptions about the inputs that market participants would use in pricing the asset or liability and are developed based on the best information available in the circumstances. The fair value hierarchy applies only to the valuation inputs used in determining the reported fair value of the investments and is not a measure of the investment credit quality. The three levels of the fair value hierarchy are described below:

•

Level 1 – Valuations based on unadjusted quoted prices in active markets for identical assets or liabilities that the Company has the ability to access at the measurement date

•

Level 2 – Valuations based on quoted prices for similar assets or liabilities in markets that are not active or for which all significant inputs are observable, either directly or indirectly

•

Level 3 – Valuations that require inputs that reflect the Company’s own assumptions that are both significant to the fair value measurement and unobservable

To the extent that a valuation is based on models or inputs that are less observable or unobservable in the market, the determination of fair value requires more judgment. Accordingly, the degree of judgment exercised by the Company in determining fair value is greatest for instruments categorized in Level 3. A financial instrument’s level within the fair value hierarchy is based on the lowest level of any input that is significant to the fair value measurement. There were no transfers within the fair value hierarchy in the years ended December 31, 2018 and 2017. The assets of the Company measured at fair value on a recurring basis as of December 31, 2018 and 2017 are summarized below:

	Fair Value Measurements Using
	Level 1		Level 2		Level 3		Total
December 31, 2018
Assets:
Cash and cash equivalents	$	62,614,010	$	—	$	—	$	62,614,010
Total assets	$	62,614,010	$	—	$	—	$	62,614,010
December 31, 2017
Assets:
Cash and cash equivalents	$	20,264,109	$	—	$	—	$	20,264,109
Total assets	$	20,264,109	$	—	$	—	$	20,264,109

Concentrations of Credit Risk and Off-Balance Sheet Risk

Cash and cash equivalents are the only financial instruments that potentially subject the Company to concentrations of credit risk. At December 31, 2018 and 2017, the Company maintains its cash and cash equivalents with high-quality, accredited financial institutions and, accordingly, such funds are subject to minimal credit risk. The Company has no significant off-balance sheet concentrations of credit risk, such as foreign currency exchange contracts, option contracts, or other hedging arrangements.

Comprehensive Loss

Comprehensive loss is defined as the change in equity of a business enterprise during a period from transactions and other events and circumstances from non-owner sources, if any. Comprehensive loss equaled net loss for all periods presented.

Furniture and Equipment

Furniture and equipment is stated at cost, less accumulated depreciation. Furniture and equipment is depreciated using the straight-line method over the estimated useful lives of the assets, generally three to seven years. Such costs are periodically reviewed for recoverability when impairment indicators are present. Such indicators include, among other factors: operating losses, unused capacity, market value declines and technological obsolescence. Recorded values of asset groups of furniture and equipment that are not expected to be recovered through undiscounted future net cash flows are written down to current fair value, which generally is determined from estimated discounted future net cash flows (assets held for use) or net realizable value (assets held for sale).

Recent Accounting Pronouncements

From time to time, new accounting pronouncements are issued by the FASB or other standard setting bodies and adopted by the Company as of the specified effective date. Unless otherwise discussed, the Company believes the impact of recently issued standards that are not yet effective will not have a material impact on its consolidated financial position or results of operations upon adoption.

In May 2014, the FASB issued amended guidance for revenue recognition, ASU 2014-09, “Revenue from Contracts with Customers (Topic 606).” This ASU outlines a single comprehensive model for entities to use in accounting for revenue arising from contracts with customers. The core principle of the guidance is that an entity should recognize revenue for the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods and services. Additionally, the ASU requires improved disclosure to help users of financial statements better understand the nature, amount, timing and uncertainty of revenue that is recognized. The Company adopted the new guidance on January 1, 2018, as discussed in Footnote 15.

In February 2016, the FASB issued ASU 2016-02, “Leases.” This ASU will require lessees to recognize almost all leases on the balance sheet as a right-of-use asset and a lease liability. For statement of operations purposes, the FASB retained a dual model, requiring leases to be classified as finance leases or operating leases. In July 2018, the FASB issued ASU No. 2018-11, Leases (Topic 842): Targeted Improvements, to provide an additional transition method options available to registrants. In accordance with Topic 842, a registrant can elect not to present comparative financial information under Topic 842 if it recognizes a cumulative-effect adjustment to retained earnings upon adoption. The Company intends to make this transition election. Additionally, the Company will elect the package of practical expedients permitted under the transition guidance within the new standard, which among other things, allows the Company to carryforward the historical lease classification. The amendments in Topic 842 are effective for the Company for fiscal years beginning with 2019, including interim periods within that year, with early adoption permitted. The Company has performed an assessment of the impact of the adoption of the amendments within Topic 842 on the Company's consolidated balance sheet for the Company's leases, which primarily consist of facility leases. Based on the Company’s assessment, the estimated impact of the adoption of Topic 842 will result in the recognition of approximately $550,000 to $600,000 of right-of-use assets and lease liabilities as of January 1, 2019 on the consolidated balance sheet. The right-of-use assets and lease liabilities are based on the present value of future minimum lease payments defined within the corresponding facility lease agreements. The impact from the adoption of Topic 842 to the Company's accumulated deficit as of January 1, 2019 or post adoption impact to our consolidated statement of operations and comprehensive loss is not expected to be material.

In March 2016, the FASB issued ASU 2016-09, “Improvements to Employee Share-Based Payment Accounting.” This ASU is intended to simplify accounting for share-based payments and requires that excess tax benefits for share-based payments be recorded as a reduction of income tax expense and reflected within operating cash flows rather than being recorded within equity and reflected within financing cash flows. The ASU also provides an option for companies to recognize forfeitures as they occur rather than estimating the number of awards expected to be forfeited. The Company adopted this ASU on January 1, 2017 and has applied the new guidance related to excess tax benefits on a prospective basis. The Company also elected to account for forfeitures of share-based payments as they occur. The adoption of this ASU was not material to the consolidated financial statements.

In August 2016, the FASB issued ASU 2016-15, “Statement of Cash Flows (Topic 230).” The objective of this ASU is to provide additional guidance and reduce diversity in practice when classifying certain transactions within the statement of cash flows. The Company adopted this ASUs as of January 1, 2018. The adoption of this ASUs did not have a material impact on the Company’s consolidated financial statements.

In November 2016, the FASB issued ASU 2016-18, “Statement of Cash Flows (Topic 230): Restricted Cash.” This ASU requires that the statement of cash flows explain the change during the period in the total of cash, cash equivalents, and amounts generally described as restricted cash or restricted cash equivalents. These ASUs are effective for financial statements issued for fiscal years beginning after December 15, 2017, including interim periods within those fiscal years. The Company adopted these ASUs as of January 1, 2018. The adoption of these ASUs did not have a material impact on the Company’s consolidated financial statements.

In May 2017, the FASB issued ASU 2017-09, “Stock Compensation - Scope of Modification Accounting.” This ASU provides clarification around which changes to the terms or conditions of a share-based payment award require the application of modification accounting under ASC 718. The Company adopted this ASU as of January 1, 2018. The adoption of this ASU did not have a material impact on the Company’s consolidated financial statements.

In June 2018, the FASB issued ASU 2018-07, “Improvements to Nonemployee Share-Based Payment Accounting.” This ASU improves financial reporting for share-based payments issued to nonemployees under ASC 718 by expanding the scope of the employee share-based payments guidance to include share-based payments issued to nonemployees. The amendments in this ASU are effective for public companies for fiscal years beginning after December 31, 2018, including interim periods within that fiscal year. The adoption of this ASU is not anticipated to have a material impact on the Company’s consolidated financial statements.

Stock-Based Compensation

12 Months Ended

Dec. 31, 2018

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Stock-Based Compensation

7. Stock-Based Compensation

In March 2017, the Company’s Board of Directors adopted, and the stockholders approved, the 2017 Stock Option and Incentive Plan (the “2017 Plan”), that became effective in April 2017. The 2017 Plan provides for the issuance of incentive awards up to 4,600,000 shares of common stock to officers, employees, consultants and directors, less the number of shares subject to issued and outstanding awards under the Aerpio Therapeutics, Inc. 2011 Equity Incentive Plan (the “2011 Plan”) that were assumed in the Merger. The 2017 Plan also provides that the number of shares reserved for issuance thereunder will be increased annually on the first day of each year beginning in 2018 by four percent (4%) of the shares of our common stock outstanding on the last day of the immediately preceding year or such smaller increase as determined by our Board of Directors. In April 2018, the Company’s Board of Directors approved a 4% increase adding 1,082,802 shares to the 2017 Plan.

Stock Options

The options granted generally vest over 48 months. Under the 2017 Plan, options vest in installments of 25% at the one-year anniversary and thereafter in 36 equal monthly installments beginning on the 1^st of the month after the one-year anniversary date, subject to the employee’s continuous service with the Company. The options generally expire ten years after the date of grant. The fair value of the options at the date of grant is recognized as an expense over the requisite service period.

During the years ended December 31, 2018 and 2017, 1,615,200 and 1,014,018 option awards were granted, respectively. In 2017, two inducement grants for 733,570 shares related to hiring the CEO and CFO and three option awards for 280,448 shares were issued under the 2017 Equity Plan. All option awards granted during 2018 were under the 2017 Equity Plan. At December 31, 2018 and 2017, 2,959,562 and 3,391,960 shares were reserved for issuance under the 2017 Plan, respectively.

The following table summarizes the stock option activity during the years ended December 31, 2018 and 2017:

	Shares			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term (in Years)		Aggregate Intrinsic Value
Outstanding, January 1, 2017		927,592		$	1.70		7.48	$	1,030,217
Granted		1,014,018			5.50
Exercised		(25,729	)		1.40
Expired/cancelled		(2,901	)		2.11
Outstanding, December 31, 2017		1,912,980		$	3.72		8.24	$	2,738,704
Expected to vest, December 31, 2017		1,161,495		$	5.02		9.65	$	441,553
Options exercisable, December 31, 2017		751,485		$	1.69		6.07	$	2,297,151
Outstanding, January 1, 2018		1,912,980		$	3.72		8.24	$	2,738,704
Granted		1,615,200			3.64
Exercised		(52,099	)		1.47
Expired/cancelled		(124,949	)		3.23
Outstanding, December 31, 2018		3,351,132		$	3.73		8.24	$	142,788
Expected to vest, December 31, 2018		2,197,619		$	4.17		9.19	$	—
Options exercisable, December 31, 2018		1,153,513		$	2.90		6.37	$	142,788

Aggregate intrinsic value represents the estimated fair value of the Company’s common stock at the end of the period in excess of the weighted average exercise price multiplied by the number of options outstanding or exercisable. The aggregate intrinsic value of the options at December 31, 2018 and 2017 was $142,788 and $2,738,704, respectively.

Stock options exercised during 2018 and 2017 had an intrinsic value of $139,108 and $92,544, respectively.

For the years ended December 31, 2018 and 2017, the Company recognized compensation expense for stock options of $2,982,173 and $327,649, respectively. As of December 31, 2018, there was $3,865,709 of unrecognized compensation cost related to stock options, which is expected to be recognized over a weighted average period of 2.55 years.

The Company uses the Black-Scholes option pricing model to determine the estimated fair value for stock-based awards. For the years ended December 31, 2018 and 2017, there were 1,615,200 and 1,014,018 options granted out of the 2017 Plan, respectively, except for two option awards for 733,570 shares that were inducement grants related to hiring the CEO and CFO in December 2017. Option pricing models require the input of various assumptions, including the option’s expected life, expected dividend yield, price volatility and risk-free interest rate of the underlying stock. As there has not been significant public market activity of the Company’s Common Stock, the Company has determined the volatility assumption for options granted based on data from a peer group of companies that issued options with substantially similar terms. The expected volatility of options granted has been determined using the average of the historical volatility measures of this peer group of companies for a period equal to the expected life of the option. The risk-free interest rate is based on the rate applicable to U.S. Treasury zero-coupon issues, with remaining maturities commensurate with the expected term of the options granted in effect on the date of grant. The Company has not paid, and does not anticipate paying, cash dividends on shares of Common Stock; therefore, the expected dividend yield is assumed to be zero in the option valuation model. Accordingly, the weighted-average fair value of the options granted during the years ended December 31, 2018 and 2017, was $2.22 and $3.39, respectively. The calculation was based on the following assumptions.

	Year Ended December 31,
	2018			2017
Expected term (years)	6.07			5.94
Risk-free interest rate		2.85	%		2.19	%
Expected volatility		65.99	%		67.57	%
Expected dividend yield		—			—

Restricted Stock

Shares of restricted stock generally had similar vesting terms as stock options. A summary of the Company’s restricted stock activity and related information for the years ended December 31, 2018 and 2017 is as follows:

	Shares			Weighted Average Grant Date Fair Value
Nonvested, January 1, 2017		241,096		$	1.91
Granted		—			—
Vested		(144,274	)		1.91
Forfeited		(5,246	)		2.20
Nonvested, December 31, 2017		91,576		$	2.12

Nonvested, January 1, 2018		91,576		$	2.12
Granted		60,000			4.75
Vested		(149,243	)		3.18
Forfeited		(2,333	)		2.25
Nonvested, December 31, 2018		—		$	—

For the years ended December 31, 2018 and 2017, the Company recognized compensation expense for restricted stock of $449,689 and $321,760, respectively. As of December 31, 2018, all restricted stock had vested.

Compensation Expense Summary

The Company recognized the following compensation cost related to employee and non-employee stock-based compensation activity for the periods presented below.

	Year Ended December 31,
	2018		2017
Research and development	$	392,470	$	393,347
General and administrative		3,039,392		256,062
Total	$	3,431,862	$	649,409

The increase in compensation expense during the year ended December 31, 2018, is primarily due to vesting under the contractual terms of the option grants awarded during 2017 and 2018.

Income Taxes

12 Months Ended

Dec. 31, 2018

Income Tax Disclosure [Abstract]

Income Taxes

8. Income Taxes

The Tax Cuts and Jobs Act (“2017 Tax Act”) was signed into law on December 22, 2017. The 2017 Tax Act significantly revised the U.S. corporate tax by, among other things, lowering the statutory corporate tax rate from 35% to 21% in 2018. The Company completed its determination of the accounting implications of the 2017 Tax Act during 2018, and there was no material impact to the Company’s provision for income taxes during 2018.

The Company did not record a current or deferred income tax expense or benefit for the years ended December 31, 2018 and 2017, due to the Company’s net losses and increases in its deferred tax asset valuation allowance. A reconciliation of the statutory federal income tax with the provision for income taxes are as follows:

	Year Ended December 31,
	2018			2017
Federal tax at statutory rate	(21.00%)			(34.00%)
State and local tax at statutory rates, net of federal income tax		(4.15	)		(0.83	)
Research and development credits		(6.37	)		(1.72	)
Other		4.27			1.42
Change in valuation allowance		27.25			(17.64	)
Remeasurement of U.S. net deferred tax assets from 35% to 21%		—			52.77
Effective tax rate	0.00%			0.00%

The Company’s income tax provision was computed based on the federal statutory rate and the average state statutory rates, net of the related federal benefit.

Deferred income taxes reflect the net tax effects of temporary differences between the carrying amounts of the assets and liabilities for financial reporting purposes and the amounts used for income and for tax carryforwards, recorded at the enacted federal statutory income tax rate. Significant components of the Company’s deferred tax assets and liabilities are as follows:

	December 31,
	2018			2017
Deferred tax assets:
Net operating loss carryforwards	$	19,946,123		$	18,819,077
Accrued expenses		595,209			204,599
Stock-based compensation		603,408			96,578
Research and development credits		3,852,714			3,038,863
Other		13,276			13,953
Total deferred tax assets		25,010,730			22,173,070
Deferred tax liabilities:
Furniture and equipment		8,390			3,606
Total deferred tax liabilities		8,390			3,606
Net deferred tax assets before valuation allowance		25,002,340			22,169,464
Less valuation allowance		(25,002,340	)		(22,169,464	)
Net deferred tax asset	$	—		$	—

When realization of the deferred tax asset is more likely than not to occur, the benefit related to the deductible temporary differences attributable to operation is recognized as a reduction of income tax expense. Valuation allowances are provided against deferred tax assets when, based on all available evidence, it is considered more likely than not that some portion or all of the recorded deferred tax assets will not be realized in future periods. The Company cannot be certain that future taxable income will be sufficient to realize its deferred tax assets, and accordingly, a full valuation allowance has been provided on its net deferred tax assets. The valuation allowance increased $2,832,876 in 2018 as a result of an increase in the net operating loss (NOL) and an increase of research and development credits carryforwards and decreased $3,774,722 in 2017 primarily as a result of the changes in the 2017 Tax Act offset by an increase with allowance on the NOL carryforward. The Company continues to monitor the need for a valuation allowance based on the profitability of its future operations.

At December 31, 2018, the Company has $84,173,000 of federal NOL carryforwards with expirations between 2032 and 2038. The Company has $5,668,095 of federal NOL carryforwards with no expiration as a result of the 2017 Tax Act. Additionally, the Company has $66,253,204 of state and local NOL carryforwards with expiration between 2019and 2039. Finally, at December 31, 2018, the Company has $3,852,714 of federal research and development credit carryforwards that expire at various dates through 2039.

Under the provisions of the Internal Revenue Code, NOL and tax credit carryforwards are subject to review and possible adjustment by the Internal Revenue Service and state tax authorities until fully utilized. NOL and tax credit carryforwards may be subject to an annual limitation in the event of certain cumulative changes in the ownership interest of significant stockholders by more than 50% over a three-year period, as defined in Sections 382 and 383 of the Internal Revenue Code and similar state provisions. The amount of the annual limitation is determined based on the value of the Company immediately before the ownership change. Subsequent ownership changes may further affect the limitation in future years. The Company has not completed a study to assess whether a change of control has occurred or whether there have been multiple changes of control since the date of the Company’s formation due to the significant complexity and cost associated with such study and that there could be additional changes in control in the future. As a result, the Company is unable to estimate the effect of these limitations, if any, on the Company’s ability to utilize NOL and tax credit carryforwards in the future. A full valuation allowance has been provided against the Company’s NOL and tax credit carryforwards and, if an adjustment is required, this adjustment would be offset by an adjustment to the deferred tax asset established for the NOL and tax credit carryforwards and the valuation allowance.

The Company has not yet conducted a study to document whether its research activities may qualify for the research and development tax credit. Such a study may result in an adjustment to the Company’s research and development credit carryforwards; however, until a study is completed, and any adjustment is known, no amounts are being presented as an uncertain tax position. A full valuation allowance has been provided against the Company’s research and development credit and, if an adjustment is required, this adjustment would be offset by an adjustment to the deferred tax asset established for the research and development credit carryforwards and the valuation allowance.

As of December 31, 2018 and 2017, the Company had no accrued uncertain tax positions or associated interest or penalties and no amounts have been recognized in the Company’s consolidated statements of operations and comprehensive loss.

The Company files income tax returns in the U.S. federal jurisdiction and various state jurisdictions. All years remain open and are subject to examination by federal and state taxing authorities.

Quarterly Results (Unaudited)

12 Months Ended

Dec. 31, 2018

Quarterly Financial Data [Abstract]

Quarterly Results

10. Quarterly Results (unaudited)

The following is a summary of our unaudited quarterly results for the years ended December 31, 2018 and 2017.

	Quarter Ended
	March 31, 2018			June 30, 2018			September 30, 2018			December 31, 2018
	(unaudited)
License revenue, and other	$	—		$	1,333,333		$	18,821,953		$	2,144
Total operating expenses		7,476,648			7,369,788			7,623,916			8,868,322
(Loss) income from operations		(7,476,648	)		(6,036,455	)		11,198,037			(8,866,178	)
Other income		51,116			46,464			339,441			347,588
Net and comprehensive (loss) income attributable to common stockholders	$	(7,425,532	)	$	(5,989,991	)	$	11,537,478		$	(8,518,590	)
Net (loss) income per share attributable to common stockholders, basic and diluted	$	(0.27	)	$	(0.22	)	$	0.28		$	(0.21	)
Weighted average number of common shares used in computing net (loss) income per share:
Basic		27,045,509			27,340,914			40,527,722			40,587,928
Diluted		27,045,509			27,340,914			40,961,620			40,587,928

	Quarter Ended
	March 31, 2017			June 30, 2017			September 30, 2017			December 31, 2017
	(unaudited)
Total operating expenses	$	4,759,585		$	5,583,862		$	4,756,238		$	6,288,858
Loss from operations		(4,759,585	)		(5,583,862	)		(4,756,238	)		(6,288,858	)
Other (expense) income, net		(236,118	)		63,555			106,671			53,829
Net loss and comprehensive loss	$	(4,995,703	)	$	(5,520,307	)	$	(4,649,567	)	$	(6,235,029	)
Reconciliation to net loss attributable to common stockholders:
Net loss and comprehensive loss	$	(4,995,703	)	$	(5,520,307	)	$	(4,649,567	)	$	(6,235,029	)
Adjustment of redeemable convertible preferred stock to redemption value		(943,297	)		—			—			—
Net loss attributable to common stockholders	$	(5,939,000	)	$	(5,520,307	)	$	(4,649,567	)	$	(6,235,029	)
Net loss per share attributable to common stockholders, basic and diluted	$	(1.06	)	$	(0.21	)	$	(0.17	)	$	(0.23	)
Weighted average number of common shares used in computing net loss per share attributable to common stockholders, basic and diluted		5,605,151			26,895,164			26,926,673			26,965,293

The sum of the quarterly net loss per share attributable to common stockholders may not equal the annual amounts reported because per share amounts are computed independently for each quarter and for full year based on respective weighted-average common shares outstanding and other dilutive potential common stockholders.

The diluted EPS calculation for the three months ended September 30, 2018 includes the dilutive common share impact of 426,860 options to purchase common stock and 7,038 unvested restricted stock. Furthermore, the diluted EPS calculation for the three months ended September 30, 2018 excludes 2.4 million options to purchase common stock that was outstanding but unvested and the effect of weighted average common stock share equivalents of 0.1 million for options to purchase common stock and 0.3 million for warrants to purchase common stock as their effect is anti-dilutive. Holders of non-vested stock-based compensation awards do not have voting rights. Diluted and Basic weighted average number of common shares were the exact same in every other period presented within the table above.

Summary of Significant Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2018

Accounting Policies [Abstract]

Basis of Presentation

The Company’s consolidated financial statements are prepared in accordance with U.S. GAAP and stated in U.S. dollars.

Segment Information

Use of Estimates

Cash and Cash Equivalents

Revenue Recognition

Upfront License Fees

Development Milestone Payments

Sales-based Milestone and Royalty Payments

Grant Income

Grant income is recognized as earned based on contract work performed.

Research and Development

Patents

Costs incurred in connection with the application for and issuances of patents are expensed as incurred.

Income Taxes

Net Loss per Share Attributable to Common Stockholders

Stock-Based Compensation

Fair Value of Financial Instruments

•

Level 1 – Valuations based on unadjusted quoted prices in active markets for identical assets or liabilities that the Company has the ability to access at the measurement date

•

Level 2 – Valuations based on quoted prices for similar assets or liabilities in markets that are not active or for which all significant inputs are observable, either directly or indirectly

•

Level 3 – Valuations that require inputs that reflect the Company’s own assumptions that are both significant to the fair value measurement and unobservable

	Fair Value Measurements Using
	Level 1		Level 2		Level 3		Total
December 31, 2018
Assets:
Cash and cash equivalents	$	62,614,010	$	—	$	—	$	62,614,010
Total assets	$	62,614,010	$	—	$	—	$	62,614,010
December 31, 2017
Assets:
Cash and cash equivalents	$	20,264,109	$	—	$	—	$	20,264,109
Total assets	$	20,264,109	$	—	$	—	$	20,264,109

Concentrations of Credit Risk and Off-Balance Sheet Risk

Comprehensive Loss

Furniture and Equipment

Recent Accounting Pronouncements

Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2018

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Summary of Stock Option Activity

The following table summarizes the stock option activity during the years ended December 31, 2018 and 2017:

	Shares			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term (in Years)		Aggregate Intrinsic Value
Outstanding, January 1, 2017		927,592		$	1.70		7.48	$	1,030,217
Granted		1,014,018			5.50
Exercised		(25,729	)		1.40
Expired/cancelled		(2,901	)		2.11
Outstanding, December 31, 2017		1,912,980		$	3.72		8.24	$	2,738,704
Expected to vest, December 31, 2017		1,161,495		$	5.02		9.65	$	441,553
Options exercisable, December 31, 2017		751,485		$	1.69		6.07	$	2,297,151
Outstanding, January 1, 2018		1,912,980		$	3.72		8.24	$	2,738,704
Granted		1,615,200			3.64
Exercised		(52,099	)		1.47
Expired/cancelled		(124,949	)		3.23
Outstanding, December 31, 2018		3,351,132		$	3.73		8.24	$	142,788
Expected to vest, December 31, 2018		2,197,619		$	4.17		9.19	$	—
Options exercisable, December 31, 2018		1,153,513		$	2.90		6.37	$	142,788

Stock Options Valuation Assumptions

The calculation was based on the following assumptions.

	Year Ended December 31,
	2018			2017
Expected term (years)	6.07			5.94
Risk-free interest rate		2.85	%		2.19	%
Expected volatility		65.99	%		67.57	%
Expected dividend yield		—			—

Summary of Restricted Stock Activity

A summary of the Company’s restricted stock activity and related information for the years ended December 31, 2018 and 2017 is as follows:

	Shares			Weighted Average Grant Date Fair Value
Nonvested, January 1, 2017		241,096		$	1.91
Granted		—			—
Vested		(144,274	)		1.91
Forfeited		(5,246	)		2.20
Nonvested, December 31, 2017		91,576		$	2.12

Nonvested, January 1, 2018		91,576		$	2.12
Granted		60,000			4.75
Vested		(149,243	)		3.18
Forfeited		(2,333	)		2.25
Nonvested, December 31, 2018		—		$	—

Summary of Recognized Compensation Cost Related to Employee and Non-employee Stock-Based Compensation Activity

The Company recognized the following compensation cost related to employee and non-employee stock-based compensation activity for the periods presented below.

	Year Ended December 31,
	2018		2017
Research and development	$	392,470	$	393,347
General and administrative		3,039,392		256,062
Total	$	3,431,862	$	649,409

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2018

Income Tax Disclosure [Abstract]

Schedule of Reconciliation of Statutory Federal Income Tax

A reconciliation of the statutory federal income tax with the provision for income taxes are as follows:

	Year Ended December 31,
	2018			2017
Federal tax at statutory rate	(21.00%)			(34.00%)
State and local tax at statutory rates, net of federal income tax		(4.15	)		(0.83	)
Research and development credits		(6.37	)		(1.72	)
Other		4.27			1.42
Change in valuation allowance		27.25			(17.64	)
Remeasurement of U.S. net deferred tax assets from 35% to 21%		—			52.77
Effective tax rate	0.00%			0.00%

Schedule of Significant Components of Deferred Tax Assets and Liabilities

Significant components of the Company’s deferred tax assets and liabilities are as follows:

	December 31,
	2018			2017
Deferred tax assets:
Net operating loss carryforwards	$	19,946,123		$	18,819,077
Accrued expenses		595,209			204,599
Stock-based compensation		603,408			96,578
Research and development credits		3,852,714			3,038,863
Other		13,276			13,953
Total deferred tax assets		25,010,730			22,173,070
Deferred tax liabilities:
Furniture and equipment		8,390			3,606
Total deferred tax liabilities		8,390			3,606
Net deferred tax assets before valuation allowance		25,002,340			22,169,464
Less valuation allowance		(25,002,340	)		(22,169,464	)
Net deferred tax asset	$	—		$	—

Quarterly Results (Unaudited) (Tables)

12 Months Ended

Dec. 31, 2018

Quarterly Financial Information Disclosure [Abstract]

Summary of Quarterly Results

The following is a summary of our unaudited quarterly results for the years ended December 31, 2018 and 2017.

	Quarter Ended
	March 31, 2018			June 30, 2018			September 30, 2018			December 31, 2018
	(unaudited)
License revenue, and other	$	—		$	1,333,333		$	18,821,953		$	2,144
Total operating expenses		7,476,648			7,369,788			7,623,916			8,868,322
(Loss) income from operations		(7,476,648	)		(6,036,455	)		11,198,037			(8,866,178	)
Other income		51,116			46,464			339,441			347,588
Net and comprehensive (loss) income attributable to common stockholders	$	(7,425,532	)	$	(5,989,991	)	$	11,537,478		$	(8,518,590	)
Net (loss) income per share attributable to common stockholders, basic and diluted	$	(0.27	)	$	(0.22	)	$	0.28		$	(0.21	)
Weighted average number of common shares used in computing net (loss) income per share:
Basic		27,045,509			27,340,914			40,527,722			40,587,928
Diluted		27,045,509			27,340,914			40,961,620			40,587,928

	Quarter Ended
	March 31, 2017			June 30, 2017			September 30, 2017			December 31, 2017
	(unaudited)
Total operating expenses	$	4,759,585		$	5,583,862		$	4,756,238		$	6,288,858
Loss from operations		(4,759,585	)		(5,583,862	)		(4,756,238	)		(6,288,858	)
Other (expense) income, net		(236,118	)		63,555			106,671			53,829
Net loss and comprehensive loss	$	(4,995,703	)	$	(5,520,307	)	$	(4,649,567	)	$	(6,235,029	)
Reconciliation to net loss attributable to common stockholders:
Net loss and comprehensive loss	$	(4,995,703	)	$	(5,520,307	)	$	(4,649,567	)	$	(6,235,029	)
Adjustment of redeemable convertible preferred stock to redemption value		(943,297	)		—			—			—
Net loss attributable to common stockholders	$	(5,939,000	)	$	(5,520,307	)	$	(4,649,567	)	$	(6,235,029	)
Net loss per share attributable to common stockholders, basic and diluted	$	(1.06	)	$	(0.21	)	$	(0.17	)	$	(0.23	)
Weighted average number of common shares used in computing net loss per share attributable to common stockholders, basic and diluted		5,605,151			26,895,164			26,926,673			26,965,293

Nature of Organization and Operations - Additional Information (Detail)				12 Months Ended
	Jul. 02, 2018 USD ($) shares	Jun. 28, 2018 shares	Mar. 15, 2017 USD ($) $ / shares shares	Dec. 31, 2018 USD ($) $ / shares shares	Dec. 31, 2017 USD ($) $ / shares shares	Mar. 14, 2017 shares	Mar. 10, 2017 $ / shares shares	Mar. 03, 2017 $ / shares shares	Dec. 31, 2016 USD ($)
Class Of Stock [Line Items]
Common stock, shares authorized				300,000,000	300,000,000		300,000,000	100,000,000
Common stock, par value \| $ / shares				$ 0.0001	$ 0.0001		$ 0.0001	$ 0.0001
Preferred stock, shares authorized				10,000,000	10,000,000		10,000,000	10,000,000
Preferred stock, par value \| $ / shares				$ 0.0001	$ 0.0001		$ 0.0001	$ 0.0001
Capital stock conversion basis ratio			2.3336572
Common stock, shares outstanding				40,588,004	27,070,038
Warrants issued to purchase common stock, exercise price \| $ / shares				$ 5.00	$ 5.00
Underwriting discounts and commissions and offering expenses paid \| $				$ 3,502,543	$ 3,084,385
Proceeds from sale of common stock \| $				51,621,570	40,247,777
Cash and cash equivalents \| $				$ 62,614,010	$ 20,264,109				$ 1,609,694
Minimum [Member]
Class Of Stock [Line Items]
Percentage of Interest owned in the combined enterprise			50.00%
2018 Public Offering [Member]
Class Of Stock [Line Items]
Common stock sold in offering		11,688,000
Underwriting discounts and commissions and offering expenses paid \| $	$ 3,500,000
Proceeds from sale of common stock \| $	$ 48,100,000
Underwriters’ Exercise of Option [Member]
Class Of Stock [Line Items]
Common stock sold in offering	1,720,200
Common Stock [Member]
Class Of Stock [Line Items]
Common stock sold in offering				13,408,200	8,049,555
Zeta Acquisition Corp. II [Member]
Class Of Stock [Line Items]
Number of shares surrendered for cancellation			4,000,000
Common stock, shares outstanding						5,000,000
Issuance of warrants term			3 years
Number of warrants issued to purchase common stock			317,562
Warrants issued to purchase common stock, exercise price \| $ / shares			$ 5.00
Zeta Acquisition Corp. II [Member] \| Common Stock [Member]
Class Of Stock [Line Items]
Net proceeds from issuance of common stock in private placement \| $			$ 37,200,000
Zeta Acquisition Corp. II [Member] \| Common Stock [Member] \| Private Placement [Member]
Class Of Stock [Line Items]
Common stock sold in offering			8,049,555
Common stock issued to private placement, price per share \| $ / shares			$ 5.00

Stock-Based Compensation - Additional Information (Detail)	1 Months Ended		12 Months Ended
	Apr. 30, 2018 shares	Mar. 31, 2017 shares	Dec. 31, 2018 USD ($) $ / shares shares	Dec. 31, 2017 USD ($) OptionAward $ / shares shares	Dec. 31, 2016 USD ($)
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of awards granted			1,615,200	1,014,018
Aggregate intrinsic value of option outstanding \| $			$ 142,788	$ 2,738,704	$ 1,030,217
Stock options exercised, intrinsic value \| $			139,108	$ 92,544
Unrecognized compensation cost related to stock options \| $			$ 3,865,709
Weighted-average fair value of options granted \| $ / shares			$ 2.22	$ 3.39
CEO and CFO [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of awards granted				733,570
Number of option awards granted \| OptionAward				2
Stock Option [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting period			48 months
Number of awards granted			1,615,200	1,014,018
Compensation expense \| $			$ 2,982,173	$ 327,649
Weighted average period expected to be recognized			2 years 6 months 18 days
Restricted Stock [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Compensation expense \| $			$ 449,689	$ 321,760
2017 Stock Option and Incentive Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock shares available for issuance	1,082,802	4,600,000
Percentage applied to the outstanding shares as annual increase in number of shares authorized for issuance	4.00%	4.00%
Number of awards granted				280,448
Number of option awards granted \| OptionAward				3
2017 Stock Option and Incentive Plan [Member] \| Stock Option [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock shares available for issuance			2,959,562	3,391,960
Term of options to be granted			10 years
Number of awards granted			1,615,200	1,014,018
2017 Stock Option and Incentive Plan [Member] \| Stock Option [Member] \| One-year Anniversary [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting percentage			25.00%

Stock-Based Compensation - Summary of Stock Option Activity (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Shares, Outstanding at beginning balance	1,912,980	927,592
Shares, Granted	1,615,200	1,014,018
Shares, Exercised	(52,099)	(25,729)
Shares, Expired/cancelled	(124,949)	(2,901)
Shares, Outstanding at ending balance	3,351,132	1,912,980	927,592
Shares, Expected to vest	2,197,619	1,161,495
Shares, Options exercisable	1,153,513	751,485
Weighted Average Exercise Price, Outstanding at beginning balance	$ 3.72	$ 1.70
Weighted Average Exercise Price, Granted	3.64	5.50
Weighted Average Exercise Price, Exercised	1.47	1.40
Weighted Average Exercise Price, Expired/cancelled	3.23	2.11
Weighted Average Exercise Price, Outstanding at ending balance	3.73	3.72	$ 1.70
Weighted Average Exercise Price, Expected to vest	4.17	5.02
Weighted Average Exercise Price, Options exercisable	$ 2.90	$ 1.69
Weighted Average Remaining Contractual Term, Outstanding	8 years 2 months 26 days	8 years 2 months 26 days	7 years 5 months 23 days
Weighted Average Remaining Contractual Term, Expected to vest	9 years 2 months 8 days	9 years 7 months 24 days
Weighted Average Remaining Contractual Term, Options exercisable	6 years 4 months 13 days	6 years 25 days
Aggregate Intrinsic Value, Outstanding	$ 142,788	$ 2,738,704	$ 1,030,217
Aggregate Intrinsic Value, Expected to vest		441,553
Aggregate Intrinsic Value, Options exercisable	$ 142,788	$ 2,297,151

Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Line Items]
Federal tax at statutory rate	21.00%	34.00%
Current income tax expense or benefit	$ 0	$ 0
Deferred income tax expense or benefit	0	0
Increase (decrease) in valuation allowance	2,832,876	(3,774,722)
Accrued uncertain tax positions	0	0
Accrued interest and penalties on uncertain tax positions	0	$ 0
Federal [Member]
Income Tax Disclosure [Line Items]
Operating loss carryforwards	84,173,000
2017 Tax Act, net operating loss carryforwards	5,668,095
State [Member]
Income Tax Disclosure [Line Items]
Operating loss carryforwards	66,253,204
Research and Development [Member] \| Federal [Member]
Income Tax Disclosure [Line Items]
Tax credit carryforwards	$ 3,852,714
Tax credit carryforwards, expiration date	Dec. 31, 2039
Maximum [Member]
Income Tax Disclosure [Line Items]
Federal tax at statutory rate		35.00%
Maximum [Member] \| Federal [Member]
Income Tax Disclosure [Line Items]
Operating loss carryforwards, expiration date	Dec. 31, 2038
Maximum [Member] \| State [Member]
Income Tax Disclosure [Line Items]
Operating loss carryforwards, expiration date	Dec. 31, 2039
Minimum [Member] \| Federal [Member]
Income Tax Disclosure [Line Items]
Operating loss carryforwards, expiration date	Dec. 31, 2032
Minimum [Member] \| State [Member]
Income Tax Disclosure [Line Items]
Operating loss carryforwards, expiration date	Dec. 31, 2019

Quarterly Results (unaudited) - Summary of Unaudited Quarterly Results (Detail) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
License revenue, and other	$ 2,144	$ 18,821,953	$ 1,333,333						$ 20,157,430
Type of Revenue [Extensible List]	arpo:LicenseRevenueAndOtherMember	arpo:LicenseRevenueAndOtherMember	arpo:LicenseRevenueAndOtherMember						arpo:LicenseRevenueAndOtherMember
Total operating expenses	$ 8,868,322	$ 7,623,916	$ 7,369,788	$ 7,476,648	$ 6,288,858	$ 4,756,238	$ 5,583,862	$ 4,759,585	$ 31,338,674	$ 21,388,543
Loss from operations	(8,866,178)	11,198,037	(6,036,455)	(7,476,648)	(6,288,858)	(4,756,238)	(5,583,862)	(4,759,585)	(11,181,244)	(21,388,543)
Other (expense) income, net	347,588	339,441	46,464	51,116	53,829	106,671	63,555	(236,118)	784,609	(12,063)
Net and comprehensive loss					(6,235,029)	(4,649,567)	(5,520,307)	(4,995,703)	(10,396,635)	(21,400,606)
Reconciliation of net loss attributable to common stockholders:
Net and comprehensive loss					(6,235,029)	(4,649,567)	(5,520,307)	(4,995,703)	(10,396,635)	(21,400,606)
Adjustment of redeemable convertible preferred stock to redemption value								(943,297)		(943,297)
Net loss attributable to common stockholders	$ (8,518,590)	$ 11,537,478	$ (5,989,991)	$ (7,425,532)	$ (6,235,029)	$ (4,649,567)	$ (5,520,307)	$ (5,939,000)	$ (10,396,635)	$ (22,343,903)
Net loss per share attributable to common stockholders, basic and diluted	$ (0.21)	$ 0.28	$ (0.22)	$ (0.27)	$ (0.23)	$ (0.17)	$ (0.21)	$ (1.06)	$ (0.31)	$ (1.03)
Weighted average number of common shares used in computing net (loss) income per share:
Basic	40,587,928	40,527,722	27,340,914	27,045,509
Diluted	40,587,928	40,961,620	27,340,914	27,045,509
Weighted average number of common shares used in computing net loss per share attributable to common stockholders, basic and diluted					26,965,293	26,926,673	26,895,164	5,605,151	33,930,846	21,673,349

Summary of Significant Accounting Policies - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2018 USD ($) Segment	Jan. 01, 2019 USD ($)	Dec. 31, 2017 USD ($)
Summary Of Significant Accounting Policies [Line Items]
Number of operating segment \| Segment	1
Uncertain tax positions	$ 0		$ 0
Minimum [Member]
Summary Of Significant Accounting Policies [Line Items]
Furniture and equipment estimated useful lives	3 years
Minimum [Member] \| ASU 2016-02 [Member] \| Subsequent Event [Member]
Summary Of Significant Accounting Policies [Line Items]
Right-of-use asset		$ 550,000
Lease liabilities		550,000
Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Furniture and equipment estimated useful lives	7 years
Maximum [Member] \| ASU 2016-02 [Member] \| Subsequent Event [Member]
Summary Of Significant Accounting Policies [Line Items]
Right-of-use asset		600,000
Lease liabilities		$ 600,000

Accounts Payable and Accrued Expenses - Schedule of Accounts Payable and Accrued Expenses (Details) - USD ($)	Dec. 31, 2018	Dec. 31, 2017
Payables And Accruals [Abstract]
Accounts payable	$ 595,680	$ 1,276,537
Professional fees	487,923	277,217
Accrued bonus	1,877,455	833,650
Accrued vacation	90,663	69,549
Accrued project costs	2,232,014	1,069,852
Other	173,182	65,359
Total accounts payable and accrued expenses	$ 5,456,917	$ 3,592,164

Furniture and Equipment - Summary of Components of Furniture and Equipment (Detail) - USD ($)	Dec. 31, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Furniture and equipment	$ 409,580	$ 443,068
Accumulated depreciation	(311,131)	(335,845)
Furniture and equipment, net	98,449	107,223
Furniture [Member]
Property, Plant and Equipment [Line Items]
Furniture and equipment	156,928	156,928
Computers [Member]
Property, Plant and Equipment [Line Items]
Furniture and equipment	75,716	109,204
Equipment [Member]
Property, Plant and Equipment [Line Items]
Furniture and equipment	141,067	141,067
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Furniture and equipment	$ 35,869	$ 35,869

Stock-Based Compensation - Summary of Recognized Compensation Cost Related to Employee and Non-employee Stock-Based Compensation Activity (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 3,431,862	$ 649,409
Research and development [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	392,470	393,347
General and administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 3,039,392	$ 256,062

Commitments and Contingencies - Additional Information (Detail)		1 Months Ended		12 Months Ended
	Nov. 30, 2018 ft²	Mar. 31, 2018 ft²	Nov. 30, 2017 ft²	Dec. 31, 2018 USD ($) Property	Dec. 31, 2017 USD ($)
Operating Leased Assets [Line Items]
Number of property leases \| Property				3
Total operating leases rent expense \| $				$ 183,222	$ 208,478
Cincinnati, Ohio [Member]
Operating Leased Assets [Line Items]
Area of lease property		7,580
Lease expiration date		Jul. 31, 2021
Lease term				3 years
Lexington, Massachusetts [Member]
Operating Leased Assets [Line Items]
Area of lease property	4,000
Dexter, Michigan [Member]
Operating Leased Assets [Line Items]
Area of lease property			687
Lease expiration date			Oct. 31, 2019
Accrued Expenses [Member] \| Cincinnati, Ohio [Member]
Operating Leased Assets [Line Items]
Total deferred rent included in accrued expenses \| $				$ 9,340	$ 42,660

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2018	Dec. 31, 2017
Statement Of Financial Position [Abstract]
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	300,000,000	300,000,000
Common stock, shares issued	40,588,004	27,070,038
Common stock, shares outstanding	40,588,004	27,070,038

Consolidated Statements of Redeemable Convertible Preferred Stock and Stockholders' Equity (Deficit) (Parenthetical) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Statement Of Stockholders Equity [Abstract]
Payments of stock issuance cost	$ 3,502,543	$ 3,084,385

Summary of Significant Accounting Policies - Schedule of Assets Measured on Recurring Basis (Detail) - Fair Value, Measurements, Recurring [Member] - USD ($)	Dec. 31, 2018	Dec. 31, 2017
Assets:
Cash and cash equivalents	$ 62,614,010	$ 20,264,109
Total assets	62,614,010	20,264,109
Level 1 [Member]
Assets:
Cash and cash equivalents	62,614,010	20,264,109
Total assets	$ 62,614,010	$ 20,264,109

Common Stock - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Mar. 10, 2017	Mar. 03, 2017
Equity [Abstract]
Common stock, shares authorized	300,000,000	300,000,000	300,000,000	100,000,000
Common stock, par value	$ 0.0001	$ 0.0001	$ 0.0001	$ 0.0001
Dividends common stock declared or paid	$ 0
Warrants outstanding	317,562	317,562
Warrants exercise price per share	$ 5.00	$ 5.00
Warrants term	3 years	3 years
Warrants expiration date	Mar. 15, 2020	Mar. 15, 2020

Preferred Stock - Additional Information (Detail) - $ / shares	Dec. 31, 2018	Dec. 31, 2017	Mar. 10, 2017	Mar. 03, 2017
Temporary Equity Disclosure [Abstract]
Preferred stock, shares authorized	10,000,000	10,000,000	10,000,000	10,000,000
Preferred stock, par value	$ 0.0001	$ 0.0001	$ 0.0001	$ 0.0001
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0

Income Taxes - Schedule of Significant Components of Deferred Tax Assets and Liabilities (Detail) - USD ($)	Dec. 31, 2018	Dec. 31, 2017
Deferred tax assets:
Net operating loss carryforwards	$ 19,946,123	$ 18,819,077
Accrued expenses	595,209	204,599
Stock-based compensation	603,408	96,578
Research and development credits	3,852,714	3,038,863
Other	13,276	13,953
Total deferred tax assets	25,010,730	22,173,070
Deferred tax liabilities:
Furniture and equipment	8,390	3,606
Total deferred tax liabilities	8,390	3,606
Net deferred tax assets before valuation allowance	25,002,340	22,169,464
Less valuation allowance	$ (25,002,340)	$ (22,169,464)

Commitments and Contingencies - Schedule of Non-cancellable Future Minimum Lease Payments Related to Operating Leases (Detail)	Dec. 31, 2018 USD ($)
Commitments And Contingencies Disclosure [Abstract]
Operating leases, 2019	$ 257,050
Operating leases, 2020	239,781
Operating leases, 2021 and thereafter	$ 191,686

Employee Retirement Plan - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Compensation And Retirement Disclosure [Abstract]
Contributions made under Plan	$ 0	$ 0
Defined contribution plan, sponsor location [extensible list]	country:US	country:US
Defined contribution plan, tax status [extensible list]	us-gaap:QualifiedPlanMember	us-gaap:QualifiedPlanMember

Employee Bonus Plan - Additional Information (Detail) - USD ($)	Dec. 31, 2018	Dec. 31, 2017
Deferred Compensation Arrangements [Abstract]
Accrued bonus	$ 1,877,455	$ 833,650

Employee Stock Purchase Plan - Additional Information (Detail) - shares	Jun. 20, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares outstanding		3,351,132	1,912,980	927,592
Employee Stock Purchase Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares outstanding		0	0
Common Stock [Member] \| Employee Stock Purchase Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock shares available for issuance	300,000
Maximum number of shares provided for issuance	350,000
Percentage of annual increase in number of shares reserved for issuance	1.00%

License Agreement - Additional Information (Detail) - USD ($)		3 Months Ended			12 Months Ended
	Jun. 28, 2018	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Dec. 31, 2018
License Agreement [Line Items]
Cash received from license agreement	$ 20,000,000
License revenue		$ 2,144	$ 18,821,953	$ 1,333,333	$ 20,157,430
License [Member]
License Agreement [Line Items]
License revenue					$ 20,000,000