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Document and Entity Information - shares	6 Months Ended
Document and Entity Information - shares	Jun. 30, 2018	Aug. 24, 2018
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Jun. 30, 2018
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	Q2
Trading Symbol	ALLK
Entity Registrant Name	Allakos Inc.
Entity Central Index Key	0001564824
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Common Stock, Shares Outstanding		42,113,059

BALANCE SHEETS - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 19,295	$ 85,207
Investments in marketable securities	44,851	0
Prepaid expenses and other current assets	2,987	1,037
Total current assets	67,133	86,244
Property and equipment, net	3,376	445
Other long-term assets	3,716	340
Total assets	74,225	87,029
Current liabilities:
Accounts payable	1,928	1,703
Accrued expenses and other current liabilities	3,082	1,089
Total current liabilities	5,010	2,792
Other long-term liabilities	1,468	36
Total liabilities	6,478	2,828
Commitments and contingencies (Note 6)
Stockholders' deficit:
Common stock, $0.001 par value per share; 55,000 shares authorized as of June 30, 2018 and December 31, 2017; 2,530 and 2,114 shares issued and outstanding as of June 30, 2018 and December 31, 2017, respectively	3	3
Additional paid-in capital	3,158	1,803
Accumulated other comprehensive income	3
Accumulated deficit	(78,436)	(60,574)
Total stockholders’ deficit	(75,272)	(58,768)
Total liabilities, convertible preferred stock, and stockholders’ deficit	74,225	87,029
Series A Convertible Preferred Stock
Current liabilities:
Convertible preferred stock, value	43,046	42,996
Series B Convertible Preferred Stock
Current liabilities:
Convertible preferred stock, value	$ 99,973	$ 99,973

BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	55,000,000	55,000,000
Common stock, shares issued	2,529,726	2,114,000
Common stock, shares outstanding	2,529,726	2,114,000
Series A Convertible Preferred Stock
Convertible preferred stock, par value	$ 0.001	$ 0.001
Convertible preferred stock, shares authorized	26,083,081	26,083,000
Convertible preferred stock, shares issued	20,866,000	20,866,000
Convertible preferred stock, shares outstanding	20,866,000	20,866,000
Convertible preferred stock, aggregate liquidation preference	$ 46,950	$ 46,950
Series B Convertible Preferred Stock
Convertible preferred stock, par value	$ 0.001	$ 0.001
Convertible preferred stock, shares authorized	12,631,506	12,632,000
Convertible preferred stock, shares issued	10,105,000	10,105,000
Convertible preferred stock, shares outstanding	10,105,000	10,105,000
Convertible preferred stock, aggregate liquidation preference	$ 100,141	$ 100,141

STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS (unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Operating expenses
Research and development	$ 7,149	$ 3,758	$ 13,550	$ 8,122
General and administrative	2,375	840	4,683	1,453
Total operating expenses	9,524	4,598	18,233	9,575
Loss from operations	(9,524)	(4,598)	(18,233)	(9,575)
Interest income (expense), net	292	(73)	516	(137)
Other expense, net	(145)	(21)	(145)	(36)
Net loss	(9,377)	(4,692)	(17,862)	(9,748)
Unrealized gain on marketable securities, net of tax	3		3
Comprehensive loss	$ (9,374)	$ (4,692)	$ (17,859)	$ (9,748)
Net loss per common share:
Basic and diluted	$ (4.17)	$ (3.18)	$ (8.36)	$ (6.73)
Weighted-average number of common shares outstanding:
Basic and diluted	2,248	1,477	2,137	1,449

STATEMENTS OF CASH FLOWS (unaudited) - USD ($)	6 Months Ended
STATEMENTS OF CASH FLOWS (unaudited) - USD ($)	Jun. 30, 2018	Jun. 30, 2017
Cash flows from operating activities
Net loss	$ (17,862,000)	$ (9,748,000)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	119,000	113,000
Accretion of tenant improvement allowance	(21,000)	0
Stock-based compensation	1,052,000	155,000
Net amortization of premiums and discounts on marketable securities	(89,000)	0
Non-cash interest related to debt facility	0	50,000
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(2,051,000)	(234,000)
Other long-term assets	(22,000)	(250,000)
Accounts payable	(647,000)	93,000
Accrued expenses and other current liabilities	1,861,000	(200,000)
Other long-term liabilities	211,000
Net cash used in operating activities	(17,449,000)	(10,021,000)
Cash flows from investing activities
Purchases of marketable securities	(44,746,000)	0
Purchases of property and equipment	(1,650,000)	(93,000)
Net cash used in investing activities	(46,396,000)	(93,000)
Cash flows from financing activities
Proceeds from the exercise of stock options, net of repurchases	291,000	75,000
Proceeds from the repayment of recourse promissory note	50,000	0
Payments for deferred financing costs	(1,606,000)	0
Net cash provided by (used in) financing activities	(1,265,000)	75,000
Net decrease in cash, cash equivalents and restricted cash	(65,110,000)	(10,039,000)
Cash, cash equivalents and restricted cash, beginning of period	85,207,000	13,416,000
Cash, cash equivalents and restricted cash, end of period	20,097,000	3,377,000
Supplemental disclosures
Cash paid for interest	0	79,000
Noncash investing and financing items:
Property and equipment purchased in accounts payable	14,000	98,000
Lessor funded lease incentives included in property and equipment	1,386,000	0
Deferred initial public offering costs in accounts payable and accrued expenses	858,000	0
Vesting of restricted common stock subject to repurchase	$ 12,000	$ 16,000

Organization and Business	6 Months Ended
Organization and Business	Jun. 30, 2018
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Organization and Business	1. Organization and Business Allakos Inc. (“Allakos” or the “Company”) was incorporated in the state of Delaware in March 2012. Allakos is a clinical stage biopharmaceutical company focused on the development of AK002 for the treatment of eosinophil and mast cell related diseases. The Company’s primary activities to date have included establishing its facilities, recruiting personnel, conducting research and development of its product candidates and raising capital. The Company’s operations are located in San Carlos, California. Liquidity Matters Since inception, the Company has incurred net losses and negative cash flows from operations. During the six months ended June 30, 2018, the Company incurred a net loss of $17.9 million and used $17.4 million of cash in operations. At June 30, 2018, the Company had an accumulated deficit of $78.4 million and does not expect to experience positive cash flows from operating activities in the foreseeable future. The Company has financed its operations to date primarily through the sale of common stock and issuance of convertible preferred stock. Management expects to incur additional operating losses in the future as the Company continues to further develop, seek regulatory approval for and, if approved, commence commercialization of its product candidates. The Company had $64.1 million of cash, cash equivalents and marketable securities at June 30, 2018. Management believes that this amount and the net proceeds raised from the Company’s initial public offering and the concurrent private placement in July 2018 are sufficient to fund the Company’s operations for at least the next 12 months from the issuance date of these financial statements. Initial Public Offering and Related Transactions On July 23, 2018, the Company completed an initial public offering (“IPO”), selling 8,203,332 shares of common stock at an offering price of $18.00 per share. Proceeds from the IPO, net of underwriting discounts and commissions, were $137.3 million. Concurrently with the IPO, the Company completed a private placement of 250,000 shares of common stock at the IPO offering price of $18.00 per share to an existing stockholder. Proceeds from this private placement were $4.5 million. In connection with the completion of the IPO on July 23, 2018, all then outstanding shares of convertible preferred stock were converted into 30,971,627 shares of common stock. Reverse Stock Split On July 6, 2018, the Company amended its certificate of incorporation to effect a 1-for-1.25 reverse stock split of every outstanding share of its convertible preferred stock and common stock. The financial statements and accompanying notes have been retroactively restated to reflect the reverse stock split.

Summary of Significant Accounting Policies

6 Months Ended

Jun. 30, 2018

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

2. Summary of Significant Accounting Policies

Basis of Presentation

The unaudited interim financial statements have been prepared in accordance with United States generally accepted accounting principles (“U.S. GAAP”). The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the amounts and disclosures reported in the financial statements and accompanying notes.

The interim balance sheet as of June 30, 2018, the statements of operations and comprehensive loss, and statements of cash flows for the six months ended June 30, 2017 and 2018 are unaudited. The unaudited interim financial statements have been prepared on the same basis as the audited annual financial statements and reflect, in the opinion of management, all adjustments of a normal and recurring nature that are necessary for the fair presentation of the Company’s financial position as of June 30, 2018 and its results of operations and comprehensive loss for the three and six months ended June 30, 2018 and 2017 and its cash flows for the six months ended June 30, 2018 and 2017. Certain information and note disclosures normally included in annual audited financial statements prepared in accordance with U.S. GAAP have been omitted. The financial data and the other financial information disclosed in these notes to the interim financial statements are also unaudited. The results of operations for any interim period are not necessarily indicative of the results to be expected for the entire year or for any other future annual or interim period. The balance sheet as of December 31, 2017 included herein was derived from the audited financial statements as of that date. These interim financial statements should be read in conjunction with the Company’s audited financial statements included in the Company’s Prospectus that forms a part of the Company’s Registration Statement on Form S-1, which was filed with the Securities and Exchange Commission (the “SEC”) pursuant to Rule 424(b) on July 19, 2018.

Use of Estimates

Management uses significant judgment when making estimates related to common stock valuation and related stock-based compensation expense, accrued expenses related to clinical trials and deferred tax valuation allowances. Management bases its estimates on historical experience and on various other assumptions that are believed to be reasonable under the circumstances, the results of which form the basis for making judgments about the carrying values of assets and liabilities that are not readily apparent from other sources. Actual results could differ from those estimates under different assumptions or conditions, and those differences could be material to the financial position and results of operations.

Concentration of Credit Risk and Other Risks and Uncertainties

Financial instruments that potentially subject the Company to credit risk principally consist of cash, cash equivalents and marketable securities. These financial instruments are held in accounts at a single financial institution that management believes possesses high credit quality. Amounts on deposit with this financial institution have and will continue to exceed federally-insured limits. The Company has not experienced any losses on its cash deposits. Additionally, the Company’s investment policy limits its investments to certain types of securities issued by the U.S. government and its agencies.

The Company is subject to a number of risks similar to that of other early-stage biopharmaceutical companies, including, but not limited to, the need to obtain adequate additional funding, possible failure of current or future clinical trials, its reliance on third parties to conduct its clinical trials, the need to obtain regulatory and marketing approvals for its product candidates, competitive developments, the need to successfully commercialize and gain market acceptance of the Company’s product candidates, its right to develop and commercialize its product candidates pursuant to the terms and conditions of the licenses granted to the Company, protection of proprietary technology, the ability to make milestone, royalty or other payments due under licensing agreements, and the need to secure and maintain adequate manufacturing arrangements with third parties. If the Company does not successfully commercialize or partner its product candidates, it will be unable to generate product revenue or achieve profitability.

Cash, Cash Equivalents and Restricted Cash

The Company considers all highly liquid investments with original maturities of three months or less from the date of purchase to be cash equivalents. Restricted cash as of June 30, 2018 represents deposits restricted from withdrawal and held by a bank in the form of collateral for an irrevocable standby letter of credit held as security for the lease of the Company’s facility in Redwood City, California. The following table provides a reconciliation of cash, cash equivalents and restricted cash reported within the Company’s balance sheets and which, in aggregate, represent the amounts reported in the accompanying statements of cash flows (in thousands):

	June 30,		December 31,
	2018		2017
Cash and cash equivalents	$	19,295	$	85,207
Restricted cash in long term assets, deposit for lease facility		802		—
Total cash, cash equivalents and restricted cash	$	20,097	$	85,207

The Company had no restricted cash at June 30, 2017 and December 31, 2016.

Marketable Securities

The Company invests in marketable securities, primarily securities issued by the U.S. government and its agencies. Investments with contractual maturities greater than 90 days that mature less than one year from the balance sheet date are classified as short-term investments. Those investments with a contractual maturity date greater than one year are considered long-term investments. Unrealized gains and losses are excluded from earnings and are reported as a component of accumulated comprehensive income (loss). The cost of securities sold is determined using the specific-identification method. Interest earned and adjustments for the amortization of premiums and discounts on investments are included in interest income (expense), net, on the statements of operations and comprehensive loss. Realized gains and losses and declines in fair value judged to be other than temporary, if any, on investments in marketable securities are included in other income (expense), net, on the statements of operations and comprehensive loss.

Fair Value Measurements

The Company accounts for fair value of its financial instruments in accordance with Financial Accounting Standards Board (the “FASB”) Accounting Standards Codification (“ASC”) Topic No. 820, Fair Value Measurements (“ASC 820”). ASC 820 establishes a common definition for fair value, establishes a framework for measuring fair value and expands disclosures about such fair value measurements. Additionally, ASC 820 defines fair value as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date.

The Company measures fair value based on a three-level hierarchy of inputs, of which the first two are considered observable and the last unobservable. Unobservable inputs reflect the Company’s own assumptions about current market conditions. The three-level hierarchy of inputs is as follows:

Level 1 – Quoted prices in active markets for identical assets or liabilities.

Level 2 – Inputs other than Level 1 that are observable, either directly or indirectly, such as quoted prices for similar assets or liabilities; quoted prices in markets that are not active; or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities.

Level 3 – Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of assets or liabilities.

To the extent that the 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.

The carrying amounts reflected in the Company’s balance sheets for cash and cash equivalents, prepaid expenses and other current assets and other long-term assets approximate fair value, due to their short-term nature.

Deferred Initial Public Offering Costs

Costs incurred in connection with the IPO primarily consist of direct incremental legal, printing and accounting fees. IPO costs are capitalized as incurred and will be offset against proceeds upon consummation of the offering. In the event the offering had been terminated or abandoned, deferred IPO costs would have been expensed in the period such determination had been made. As of June 30, 2018 and December 31, 2017, there was $2.6 million and $0.2 million, respectively, of deferred IPO costs included in other long-term assets on the Company’s balance sheets.

Lease Liabilities

The Company classifies the agreements for its office and laboratory facilities as an operating lease. Rent expense is recorded on a straight-line basis over the term of the lease. Differences that exist between cash rent payments and the recognition of rent expense, such as those resulting from rent abatements or contractual escalations of minimum lease payments, are recorded as a deferred rent liability and recognized as adjustments to rental expense on a straight-line basis over the term of the lease. The current portion of the deferred rent liability is included within accrued expenses and other current liabilities on the Company’s balance sheets. Noncurrent portion of deferred rent liability is classified as other long-term liabilities. Tenant improvement allowances received are recorded as lease incentive obligations included in accrued expenses and other current liabilities and other long-term liabilities on the Company’s balance sheets and are amortized to rent expense over the term of the lease.

Term Loan Financing Costs

During the three months and six months ended June 30, 2017, the Company recognized noncash interest expense of $25,000 and $50,000, respectively, related to its then outstanding debt facility. Noncash interest included the amortization and accretion of various costs incurred in connection with the issuance of the associated debt instruments and calculated using the effective interest rate method over the expected term of the debt. In December 2017, the Company repaid all outstanding debt. Noncash interest expense is included in interest income (expense), net, within the Company’s statements of operations and comprehensive loss.

Research and Development Expense

Research and development costs are expensed as incurred. Research and development costs include, among others, consulting costs, salaries, benefits, travel, stock-based compensation, laboratory supplies and other non-capital equipment utilized for in-house research, allocation of facilities and overhead costs and external costs paid to third parties that conduct research and development activities on the Company’s behalf. Amounts incurred in connection with license agreements are also included in research and development expense.

Advance payments for goods or services to be rendered in the future for use in research and development activities are deferred and included in prepaid expenses and other current assets. The deferred amounts are expensed as the related goods are delivered or the services are performed.

Accrued Research and Development Costs

Service agreements with contract research organizations (“CROs”) and contract development and manufacturing organizations (“CDMOs”) comprise a significant component of the Company’s research and development activities. External costs for CROs and CDMOs are recognized as the services are incurred. The Company accrues for expenses resulting from obligations under agreements with its third parties for which the timing of payments does not match the periods over which the materials or services are provided to the Company. Accruals are recorded based on estimates of services received and efforts expended pursuant to agreements established with CROs, CDMOs and other outside service providers. These estimates are typically based on contracted amounts applied to the proportion of work performed and determined through analysis with internal personnel and external service providers as to the progress or stage of completion of the services.

The Company makes judgements and estimates in determining the accrual balance in each reporting period. In the event advance payments are made to a CRO, CDMO or other outside service provider, the payments are recorded within prepaid expenses and other current assets and subsequently recognized as research and development expense when the associated services have been performed. As actual costs become known, the Company adjusts its liabilities and assets. Inputs, such as the extent of services received and the duration of services to be performed, may vary from the Company’s estimates, which will result in adjustments to research and development expense in future periods. Changes in these estimates that result in material changes to the Company’s accruals could materially affect the Company’s results of operations. The Company’s historical estimates have not been materially different from actual amounts recorded.

Convertible Preferred Stock

The Company recorded all shares of convertible preferred stock net of offering costs at their respective fair values on the dates of issuance. The convertible preferred stock was recorded outside of stockholders’ deficit because, in the event of certain deemed liquidation events considered not solely within the Company’s control, such as a merger, acquisition or sale of all or substantially all of the Company’s assets, the convertible preferred stock will become redeemable at the option of the holders. In the event of a change of control of the Company, proceeds received from the sale of such shares will be distributed in accordance with the liquidation preferences set forth in the Company’s Second Amended and Restated Certificate of Incorporation unless the holders of convertible preferred stock had previously converted their shares of convertible preferred stock into shares of common stock. In connection with the completion of the IPO on July 23, 2018, all then outstanding shares of convertible preferred stock were converted into 30,971,627 shares of common stock.

Stock-Based Compensation

The Company accounts for its stock-based compensation in accordance with FASB ASC Topic 718, Compensation—Stock Compensation. ASC Topic 718 requires all stock-based payments to employees and directors to be recognized as expense in the statements of operations and comprehensive loss based on their grant date fair values. For purposes of determining the estimated fair value of stock options granted to employees and directors, the Company uses the Black-Scholes option pricing model. The Black-Scholes option pricing model requires the input of certain assumptions that involve judgment, for which changes can materially affect the resulting estimates of fair value. The assumptions used to determine the fair value of stock options granted were as follows:

Expected volatility – Due to the lack of a public market for the Company’s common stock and a lack of company-specific historical and implied volatility data, the Company has based its computation of expected volatility on the historical volatility of a representative group of public companies with similar characteristics to the Company, including stage of product development and life science industry focus. The historical volatility is calculated based on a period of time commensurate with the expected term assumption.

Expected term – The Company determines the expected term in accordance with the “simplified method” described by SEC Staff Accounting Bulletin No. 107, Share-Based Payment, as it does not have sufficient historical exercise data to provide a reasonable basis upon which to estimate the expected term.

Risk-free interest rate – The Company bases the risk-free interest rate on United States Treasury securities with terms consistent to the expected term of the stock option being valued.

Expected dividends – The expected dividend yield is assumed to be zero as the Company has never paid dividends and has no current plans to pay any dividends on its common stock.

The Company uses historical data to estimate pre-vesting forfeitures and records stock-based compensation expense only for those awards expected to vest. To the extent that actual forfeitures differ from estimates, the difference is recorded as a cumulative adjustment in the period the estimates are revised. The Company expenses the fair value of its stock-based compensation awards to employees on a straight-line basis over the requisite service period, which is generally the vesting period.

Comprehensive Loss

Comprehensive loss is defined as the change in stockholders’ equity (deficit) during a period from transactions and other events and circumstances from non-owner sources and consists primarily of unrealized gains and losses on the Company’s investments in marketable securities.

Net Loss per Share

The Company calculates basic net loss per share by dividing the net loss attributable to common stockholders by the weighted-average shares of common stock outstanding during the period. The Company calculates diluted net loss per share after giving consideration to all potentially dilutive securities outstanding during the period using the treasury-stock and if-converted methods, except where the effect of including such securities would be anti-dilutive. Because the Company has reported net losses since inception, the effect from potentially dilutive securities would have been anti-dilutive and therefore has been excluded from the calculation of diluted net loss per share.

Basic and diluted net loss per share was calculated as follows (in thousands, except per share data):

	Three Months Ended						Six Months Ended
	June 30,						June 30,
	2018			2017			2018			2017
Numerator:
Net loss	$	(9,377	)	$	(4,692	)	$	(17,862	)	$	(9,748	)
Denominator:
Weighted-average shares of common stock outstanding, basic and diluted		2,248			1,477			2,137			1,449
Net loss per share, basic and diluted	$	(4.17	)	$	(3.18	)	$	(8.36	)	$	(6.73	)

The following table sets forth the potentially dilutive securities that have been excluded from the calculation of diluted net loss per share due to their anti-dilutive effect for the periods indicated (in thousands):

	Three and Six Months Ended
	June 30,
	2018		2017
Series A convertible preferred stock		20,866		20,866
Series B convertible preferred stock		10,105		—
Options to purchase common stock		6,529		4,666
Warrants to purchase common stock		48		48
Unvested restricted common stock		76		167
Total		37,624		25,747

Recent Accounting Pronouncements

In February 2016, the FASB issued Accounting Standards Update (“ASU”) No. 2016-02, Leases (“ASU 2016-02”). ASU 2016-02 requires an entity to recognize assets and liabilities arising from a lease for both financing and operating leases. ASU 2016-02 will also require new qualitative and quantitative disclosures to help investors and other financial statement users better understand the amount, timing and uncertainty of cash flows arising from leases. For public entities, ASU 2016-02 is effective for fiscal years beginning after December 15, 2018. Early adoption is permitted. The Company is currently evaluating the impact of the adoption of this ASU and anticipates the recognition of additional assets and corresponding liabilities on its balance sheets related to leases.

In November 2016, the FASB issued ASU No. 2016-18, Statement of Cash Flows: Restricted Cash (“ASU 2016-18”). ASU 2016-18 amends the classification and presentation of changes in restricted cash or restricted cash equivalents in the statement of cash flows. ASU 2016-18 is effective for public business entities for fiscal years beginning after December 15, 2017, and interim periods within those fiscal years. The Company adopted ASU 2016-18 retrospectively as of January 1, 2018. There was no significant impact to the Company’s financial statements as there were no restricted cash or restricted cash equivalent balances in the prior periods.

Fair Value Measurements

6 Months Ended

Jun. 30, 2018

Fair Value Disclosures [Abstract]

Fair Value Measurements

3. Fair Value Measurements

The Company measures and reports certain financial instruments as assets and liabilities at fair value on a recurring basis. The Company’s financial assets measured at fair value on a recurring basis were as follows (in thousands):

	June 30, 2018
	Level 1		Level 2		Level 3		Total
Cash equivalents	$	13,771	$	—	$	—	$	13,771
Marketable securities
U.S. treasuries		—		44,851		—		44,851
Total cash equivalents and marketable securities	$	13,771	$	44,851	$	—	$	58,622

	December 31, 2017
	Level 1		Level 2		Level 3		Total
Cash equivalents	$	82,526	$	—	$	—	$	82,526
Total cash equivalents	$	82,526	$	—	$	—	$	82,526

The Company evaluates transfers between levels at the end of each reporting period. There were no transfers of assets or liabilities between levels during the three and six months ended June 30, 2018 and 2017.

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

Marketable Securities

6 Months Ended

Jun. 30, 2018

Investments Debt And Equity Securities [Abstract]

Marketable Securities

4. Marketable Securities

All marketable securities were considered available-for-sale at June 30, 2018. The amortized cost, gross unrealized holding gains or losses, and fair value of the Company’s marketable securities by major security type at June 30, 2018 are summarized in the table below (in thousands):

	June 30, 2018
	Amortized Cost Basis		Unrealized Gains		Unrealized Losses			Fair Value
Short-term marketable securities
U.S. treasuries	$	44,848	$	4	$	(1	)	$	44,851
Total short-term marketable securities	$	44,848	$	4	$	(1	)	$	44,851

The Company had no other-than-temporary impairments on its marketable securities during the three and six months ended June 30, 2018. The Company has the intent and ability to hold all marketable securities until their maturities.

The Company held no marketable securities at December 31, 2017.

Balance Sheet Components and Supplemental Disclosures

6 Months Ended

Jun. 30, 2018

Balance Sheet Related Disclosures [Abstract]

Balance Sheet Components and Supplemental Disclosures

5. Balance Sheet Components and Supplemental Disclosures

Property and Equipment, Net

Property and equipment, net, consisted of the following (in thousands):

	June 30,			December 31,
	2018			2017
Laboratory equipment	$	1,040		$	949
Leasehold improvements		55			55
Construction in progress		2,959			—
		4,054			1,004
Less accumulated depreciation		(678	)		(559	)
Property and equipment, net	$	3,376		$	445

Depreciation and amortization expense for the three months ended June 30, 2018 and 2017 was $58,000 and $62,000, respectively. Depreciation expense for the six months ended June 30, 2018 and 2017 was $119,000 and $113,000, respectively.

Construction in progress represents direct costs related to the construction of leasehold improvements associated with the Company’s lease agreement entered into in January 2018. Costs of assets under construction are capitalized but are not depreciated until the construction is substantially complete and the assets being constructed are ready for their intended use. Depreciation is recorded using the straight-line method over the lesser of the lease term or the estimated useful lives of the leasehold improvements.

Accrued Expenses and Other Current Liabilities

Accrued expenses and other current liabilities consisted of the following (in thousands):

	June 30,		December 31,
	2018		2017
Accrued outside professional services	$	1,214	$	787
Accrued compensation		1,707		265
Other current liabilities		161		37
Total	$	3,082	$	1,089

Commitments and Contingencies

6 Months Ended

Jun. 30, 2018

Commitments And Contingencies Disclosure [Abstract]

Commitments and Contingencies

6. Commitments and Contingencies

Operating Lease Obligations

The Company’s operating lease obligations primarily relate to its leased office and laboratory space under two separate noncancelable operating leases that begin to expire in June 2019. The Company’s San Carlos lease agreement, which was amended in August 2015, includes two renewal provisions allowing the Company to extend the lease for an additional period of one year each. The amended lease agreement includes a rent abatement and escalation clauses for increased rent over the lease term.

The Company’s Redwood City lease agreement was entered into January 2018, with a contractual lease term commencing upon substantial completion and delivery of the premises. The base term of the lease is 10.75 years with an option to extend an additional term of 5 years. The lease agreement required a security deposit of $0.8 million, which the Company satisfied by establishing a letter of credit secured by restricted cash. Restricted cash is recorded in other long-term assets on the Company’s balance sheet.

The lease agreement entered into in January 2018 allows for a tenant improvement allowance of up to $1.4 million to be applied to the total cost of tenant improvements to the leased premises. Tenant improvement allowances received are recorded as lease incentive obligations included in accrued expenses and other current liabilities and other long-term liabilities on the Company’s balance sheets and are amortized to rent expense over the term of the lease. As of June 30, 2018, lease incentive obligations totaled $1.4 million.

In addition to the minimum future lease commitments presented below, both leases require the Company to pay property taxes, insurance, maintenance and repair costs. Rent expense is recognized using the straight-line method over the respective terms. The Company records a deferred rent liability calculated as the difference between rent expense and cash rental payments. The current portion of the liability is included within accrued expenses and other current liabilities on the Company’s balance sheets. The remaining non-current portion is classified in other long-term liabilities.

Future minimum lease payments required under operating leases are as follows (in thousands):

Fiscal Year Ending December 31,
2018 (remaining 6 months)	$	210
2019		741
2020		1,239
2021		1,277
2022		1,315
Thereafter		9,429
Total minimum future lease payments	$	14,211

In November 2015, the Company entered into a sublease agreement with a third party for a portion of the Company’s facilities in San Carlos, California. The sublease has a month-to-month term and can be terminated by either party with a thirty-day written notice. Sublease payments owed are recorded as an offset to the Company’s rent expense.

Net rent expense was $0.3 million and $0.1 million for the three months ended June 30, 2018 and 2017, respectively. Net rent expense was $0.4 million and $0.2 million for the six months ended June 30, 2018 and 2017, respectively.

Purchase Obligations

The Company has entered into contractual agreements with various research and development organizations and suppliers in the normal course of its business. All contracts are terminable, with varying provisions regarding termination. If a contract were to be terminated, the Company would only be obligated for the products or services that the Company had received through the time of termination as well as any non-cancelable minimum payments contractually agreed upon prior to the effective date of termination. In the case of terminating a clinical trial agreement with an investigational site conducting clinical activities on behalf of the Company, the Company would also be obligated to provide continued support for appropriate safety procedures through completion or termination of the associated study. At June 30, 2018, the Company had no non-cancelable purchase obligations under these agreements.

In-Licensing Agreements

The Company has entered into exclusive and non-exclusive, royalty bearing license agreements with third-parties for certain intellectual property. Under the terms of the license agreements, the Company is obligated to pay milestone payments upon the achievement of specified clinical, regulatory and commercial milestones. Actual amounts due under the license agreements will vary depending on factors including, but not limited to, the number of products developed and the Company’s ability to further develop and commercialize the licensed products. The Company is also subject to future royalty payments based on sales of the licensed products. In-licensing payments to third parties for milestones are recognized as research and development expense in the period of achievement.

The Company recognized $0.3 million of milestone expense for the six months ended June 30, 2018. The Company did not recognize any milestone expense during the three months ended June 30, 2018 and the three and six months ended June 30, 2017. Milestone payments are not creditable against royalties. As of June 30, 2018, the Company has not incurred any royalty liabilities related to its license agreements, as product sales have not yet commenced.

Exclusive License Agreement with The Johns Hopkins University

In December 2013, the Company entered into a license agreement with The Johns Hopkins University (“JHU”) for a worldwide exclusive license to develop, use, manufacture and commercialize covered product candidates including AK001 and AK002, which was amended in September 30, 2016. Under the terms of the agreement, the Company has made upfront and milestone payments of $0.3 million through June 30, 2018 and may be required to make aggregate additional milestone payments of up to $4.0 million. The Company also issued 88,887 shares of common stock as consideration under the JHU license agreement. In addition to milestone payments, the Company is also subject to single-digit royalties to JHU based on future net sales of each licensed therapeutic product candidate by the Company and its affiliates and sublicensees, with up to a low six digit dollar minimum annual royalty payment.

Non-exclusive License Agreement with BioWa Inc. and Lonza Sales AG

In October 2013, the Company entered into a tripartite agreement with BioWa Inc. (“BioWa”), and Lonza Sales AG (“Lonza”), for the non-exclusive worldwide license to develop and commercialize product candidates including AK002 that are manufactured using a technology jointly developed and owned by BioWa and Lonza. Under the terms of the agreement, the Company has made milestone payments of $0.4 million through June 30, 2018 and may be required to make aggregate additional milestone payments of up to $41.0 million. In addition to milestone payments, the Company is also subject to minimum annual commercial license fees of $40,000 per year to BioWa until such time as BioWa receives royalty payments, as well as low single-digit royalties to BioWa and to Lonza. Royalties are based on future net sales by the Company and its affiliates and sublicensees and vary dependent on Lonza’s participation as sole manufacturer for commercial production.

Indemnification Agreements

The Company has entered into indemnification agreements with certain directors and officers that require the Company, among other things, to indemnify them against certain liabilities that may arise by reason of their status or service as directors or officers. To date, no such matters have arisen and the Company does not believe that the outcome of any claims under indemnification arrangements will have a material adverse effect on its financial positions, results of operations or cash flows. Accordingly, the Company has not recorded a liability related to such indemnifications at June 30, 2018.

Convertible Preferred Stock and Stockholders' Deficit

6 Months Ended

Jun. 30, 2018

Stockholders Equity Note [Abstract]

Convertible Preferred Stock and Stockholders' Deficit

7. Convertible Preferred Stock and Stockholders’ Deficit

As of June 30, 2018, the Company is authorized to issue a total of 93,714,587 shares of stock. Of these shares, 38,714,587 are designated as preferred stock, including 26,083,081 Series A shares and 12,631,506 Series B shares. The Company is authorized to issue a total of 55,000,000 shares of common stock, of which 2,529,726 shares were issued and outstanding at June 30, 2018.

Common Stock

A summary of common stock shares reserved for future issuance upon the exercise, issuance or conversion of the respective equity instruments is as follows (in thousands):

	June 30,		December 31,
	2018		2017
Series A convertible preferred stock		26,083		26,083
Series B convertible preferred stock		12,632		12,632
Stock options issued and outstanding		6,529		4,884
Stock options available for future grant		285		2,346
Conversion of common stock warrants		48		48
Total		45,577		45,993

Common stockholders are entitled to dividends if and when declared by the Board of Directors subject to the prior rights of the preferred stockholders. As of June 30, 2018, no dividends on common stock had been declared by the Board of Directors.

Stock-Based Compensation

6 Months Ended

Jun. 30, 2018

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Stock-Based Compensation

8. Stock-Based Compensation

Total stock-based compensation expense recognized is as follows (in thousands):

	Three Months Ended				Six Months Ended
	June 30,				June 30,
	2018		2017		2018		2017
Research and development	$	167	$	42	$	335	$	69
General and administrative		272		67		717		86
Total	$	439	$	109	$	1,052	$	155

No income tax benefits for stock-based compensation expense have been recognized for the three and six months ended June 30, 2018 and 2017 as a result of the Company’s full valuation allowance applied to net deferred tax assets and net operating loss carryforwards.

The following weighted-average assumptions were used to calculate the fair value of stock-based awards granted to employees and directors during the periods indicated:

	Three Months Ended						Six Months Ended
	June 30,						June 30,
	2018			2017			2018			2017
Risk-free interest rate		2.93	%		1.79	%		2.66	%		1.79	%
Expected volatility		75.00	%		78.00	%		76.66	%		78.00	%
Expected dividend yield		—			—			—			—
Expected term (in years)		6.08			6.08			5.99			6.08

Activity under the 2012 Equity Incentive Plan, as amended, is summarized as follows (in thousands, except per share data):

							Weighted-
	Shares						Average
	Available			Options			Exercise
	for Grant			Outstanding			Price
Balance at December 31, 2017		2,346			4,884		$	0.67
Granted		(2,275	)		2,275		$	4.14
Exercised		—			(416	)	$	0.70
Forfeited		214			(214	)	$	0.50
Balance at June 30, 2018		285			6,529		$	1.88
Options exercisable					3,573		$	1.03
Options vested and expected to vest					6,464		$	1.88

During the three and six months ended June 30, 2018 and 2017, the Company did not grant any stock options with performance-based or market-based vesting conditions, nor did the Company grant any stock options to non-employees in exchange for services.

As of June 30, 2018, total unrecognized stock-based compensation expense relating to unvested stock options was $6.7 million. This amount is expected to be recognized over a weighted-average period of 3.0 years.

Defined Contribution Plan	6 Months Ended
Defined Contribution Plan	Jun. 30, 2018
Defined Contribution Pension And Other Postretirement Plans Disclosure [Abstract]
Defined Contribution Plan	9. Defined Contribution Plan In July 2013, the Company established a Savings Incentive Match Plan (the “SIMPLE IRA plan”) for its employees, allowing for both employee and employer contributions for those employees who meet defined minimum age and service requirements. The SIMPLE IRA plan allows participants to defer a portion of their annual compensation on a pretax basis. During the three and six months ended June 30, 2017, the Company made contributions to the SIMPLE IRA plan of $21,000 and $51,000, respectively. In January 2018, the Company terminated and replaced the SIMPLE IRA with a defined contribution plan under Section 401(k) of the Internal Revenue Code (the “401(k) plan”). The 401(k) plan covers all employees who meet defined minimum age and service requirements. Employee contributions are voluntary and are determined on an individual basis, limited to the maximum amount allowable under U.S. federal tax regulations. The Company makes matching contributions of up to 4% of the eligible employees’ compensation to the 401(k) plan. During the three and six months ended June 30, 2018, the Company made contributions to the 401(k) plan of $59,000 and $118,000, respectively.

Related Party Transactions	6 Months Ended
Related Party Transactions	Jun. 30, 2018
Related Party Transactions [Abstract]
Related Party Transactions	10. Related Party Transactions In September 2014, as part of the second closings of its Series A convertible preferred stock, the Company received a $50,000 fully recourse promissory note from an employee as partial consideration for the purchase of Series A convertible preferred stock. The loan accrues interest at 2.97% per annum and is scheduled to mature on September 19, 2024. The principal portion of the related party promissory note was recorded in temporary equity on the balance sheets as a reduction to Series A convertible preferred stock. Interest accrued on the loan was recorded as a receivable within prepaid and other current assets on the balance sheets. The related party promissory note and accrued interest was paid in full in June 2018. For the three and six months ended June 30, 2018 and 2017, the Company recognized insignificant interest income in each reporting period. Interest income related to the promissory note was included as a component of interest income (expense), net, within the Company’s statements of operations and comprehensive loss.

Subsequent Events	6 Months Ended
Subsequent Events	Jun. 30, 2018
Subsequent Events [Abstract]
Subsequent Events	11. Subsequent Events On July 6, 2018, the Company amended its certificate of incorporation to effect a 1-for-1.25 reverse stock split of every outstanding share of its convertible preferred stock and common stock. The financial statements and accompanying notes have been retroactively restated to reflect the reverse stock split. On July 23, 2018, the Company completed an IPO, selling 8,203,332 shares of common stock at an offering price of $18.00 per share. Proceeds from the IPO, net of underwriting discounts and commissions, were $137.3 million. Concurrently with the IPO, the Company completed a private placement of 250,000 shares of common stock at the IPO offering price of $18.00 per share to an existing stockholder. Proceeds from this private placement were $4.5 million. In connection with the completion of the IPO on July 23, 2018, all then outstanding shares of convertible preferred stock were converted into 30,971,627 shares of common stock.

Summary of Significant Accounting Policies (Policies)

6 Months Ended

Jun. 30, 2018

Accounting Policies [Abstract]

Basis of Presentation

Use of Estimates

Concentration of Credit Risk and Other Risks and Uncertainties

Cash, Cash Equivalents and Restricted Cash

	June 30,		December 31,
	2018		2017
Cash and cash equivalents	$	19,295	$	85,207
Restricted cash in long term assets, deposit for lease facility		802		—
Total cash, cash equivalents and restricted cash	$	20,097	$	85,207

The Company had no restricted cash at June 30, 2017 and December 31, 2016.

Marketable Securities

Fair Value Measurements

Level 1 – Quoted prices in active markets for identical assets or liabilities.

Level 3 – Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of assets or liabilities.

Deferred Initial Public Offering Costs

Lease Liabilities

Term Loan Financing Costs

Research and Development Expense

Accrued Research and Development Costs

Convertible Preferred Stock

Stock-Based Compensation

Risk-free interest rate – The Company bases the risk-free interest rate on United States Treasury securities with terms consistent to the expected term of the stock option being valued.

Expected dividends – The expected dividend yield is assumed to be zero as the Company has never paid dividends and has no current plans to pay any dividends on its common stock.

Comprehensive Loss

Net Loss per Share

Basic and diluted net loss per share was calculated as follows (in thousands, except per share data):

	Three Months Ended						Six Months Ended
	June 30,						June 30,
	2018			2017			2018			2017
Numerator:
Net loss	$	(9,377	)	$	(4,692	)	$	(17,862	)	$	(9,748	)
Denominator:
Weighted-average shares of common stock outstanding, basic and diluted		2,248			1,477			2,137			1,449
Net loss per share, basic and diluted	$	(4.17	)	$	(3.18	)	$	(8.36	)	$	(6.73	)

	Three and Six Months Ended
	June 30,
	2018		2017
Series A convertible preferred stock		20,866		20,866
Series B convertible preferred stock		10,105		—
Options to purchase common stock		6,529		4,666
Warrants to purchase common stock		48		48
Unvested restricted common stock		76		167
Total		37,624		25,747

Recent Accounting Pronouncements

Summary of Significant Accounting Policies (Tables)

6 Months Ended

Jun. 30, 2018

Accounting Policies [Abstract]

Reconciliation of Cash, Cash Equivalents and Restricted Cash

The following table provides a reconciliation of cash, cash equivalents and restricted cash reported within the Company’s balance sheets and which, in aggregate, represent the amounts reported in the accompanying statements of cash flows (in thousands):

	June 30,		December 31,
	2018		2017
Cash and cash equivalents	$	19,295	$	85,207
Restricted cash in long term assets, deposit for lease facility		802		—
Total cash, cash equivalents and restricted cash	$	20,097	$	85,207

Calculation of Basic and Diluted Net Loss per Share

Basic and diluted net loss per share was calculated as follows (in thousands, except per share data):

	Three Months Ended						Six Months Ended
	June 30,						June 30,
	2018			2017			2018			2017
Numerator:
Net loss	$	(9,377	)	$	(4,692	)	$	(17,862	)	$	(9,748	)
Denominator:
Weighted-average shares of common stock outstanding, basic and diluted		2,248			1,477			2,137			1,449
Net loss per share, basic and diluted	$	(4.17	)	$	(3.18	)	$	(8.36	)	$	(6.73	)

Summary of Potentially Dilutive Securities Excluded from Calculation of Diluted Net Loss per Share

	Three and Six Months Ended
	June 30,
	2018		2017
Series A convertible preferred stock		20,866		20,866
Series B convertible preferred stock		10,105		—
Options to purchase common stock		6,529		4,666
Warrants to purchase common stock		48		48
Unvested restricted common stock		76		167
Total		37,624		25,747

Fair Value Measurements (Tables)

6 Months Ended

Jun. 30, 2018

Fair Value Disclosures [Abstract]

Summary of Financial Assets Measured at Fair Value on Recurring Basis

	June 30, 2018
	Level 1		Level 2		Level 3		Total
Cash equivalents	$	13,771	$	—	$	—	$	13,771
Marketable securities
U.S. treasuries		—		44,851		—		44,851
Total cash equivalents and marketable securities	$	13,771	$	44,851	$	—	$	58,622

	December 31, 2017
	Level 1		Level 2		Level 3		Total
Cash equivalents	$	82,526	$	—	$	—	$	82,526
Total cash equivalents	$	82,526	$	—	$	—	$	82,526

Marketable Securities (Tables)

6 Months Ended

Jun. 30, 2018

Investments Debt And Equity Securities [Abstract]

Summary of Amortized Cost, Gross Unrealized Holding Gains or Losses, and Fair Value of Marketable Securities

	June 30, 2018
	Amortized Cost Basis		Unrealized Gains		Unrealized Losses			Fair Value
Short-term marketable securities
U.S. treasuries	$	44,848	$	4	$	(1	)	$	44,851
Total short-term marketable securities	$	44,848	$	4	$	(1	)	$	44,851

Balance Sheet Components and Supplemental Disclosures (Tables)

6 Months Ended

Jun. 30, 2018

Balance Sheet Related Disclosures [Abstract]

Schedule of Property and Equipment, Net

Property and equipment, net, consisted of the following (in thousands):

	June 30,			December 31,
	2018			2017
Laboratory equipment	$	1,040		$	949
Leasehold improvements		55			55
Construction in progress		2,959			—
		4,054			1,004
Less accumulated depreciation		(678	)		(559	)
Property and equipment, net	$	3,376		$	445

Schedule of Accrued Expenses and Other Current Liabilities

Accrued expenses and other current liabilities consisted of the following (in thousands):

	June 30,		December 31,
	2018		2017
Accrued outside professional services	$	1,214	$	787
Accrued compensation		1,707		265
Other current liabilities		161		37
Total	$	3,082	$	1,089

Commitments and Contingencies (Tables)

6 Months Ended

Jun. 30, 2018

Commitments And Contingencies Disclosure [Abstract]

Summary of Future Minimum Lease Payments Required Under Operating Leases

Future minimum lease payments required under operating leases are as follows (in thousands):

Fiscal Year Ending December 31,
2018 (remaining 6 months)	$	210
2019		741
2020		1,239
2021		1,277
2022		1,315
Thereafter		9,429
Total minimum future lease payments	$	14,211

Convertible Preferred Stock and Stockholders' Deficit (Tables)

6 Months Ended

Jun. 30, 2018

Stockholders Equity Note [Abstract]

Summary of Common Stock Shares Reserved for Future Issuance

A summary of common stock shares reserved for future issuance upon the exercise, issuance or conversion of the respective equity instruments is as follows (in thousands):

	June 30,		December 31,
	2018		2017
Series A convertible preferred stock		26,083		26,083
Series B convertible preferred stock		12,632		12,632
Stock options issued and outstanding		6,529		4,884
Stock options available for future grant		285		2,346
Conversion of common stock warrants		48		48
Total		45,577		45,993

- Definition

Tabular disclosure of an entity's stock, including par or stated value per share, number and dollar amount of share subscriptions, shares authorized, shares issued, shares outstanding, number and dollar amount of shares held in an employee trust, dividend per share, total dividends, share conversion features, par value plus additional paid in capital, the value of treasury stock and other information necessary to a fair presentation, and EPS information. Stock by class includes common, convertible, and preferred stocks which are not redeemable or redeemable solely at the option of the issuer. Includes preferred stock with redemption features that are solely within the control of the issuer and mandatorily redeemable stock if redemption is required to occur only upon liquidation or termination of the reporting entity. If more than one issue is outstanding, state the title of each issue and the corresponding dollar amount; dollar amount of any shares subscribed but unissued and the deduction of subscriptions receivable there from; number of shares authorized, issued, and outstanding.

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+ Details

Stock-Based Compensation (Tables)

6 Months Ended

Jun. 30, 2018

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Summary of Total Stock-Based Compensation Expense Recognized

Total stock-based compensation expense recognized is as follows (in thousands):

	Three Months Ended				Six Months Ended
	June 30,				June 30,
	2018		2017		2018		2017
Research and development	$	167	$	42	$	335	$	69
General and administrative		272		67		717		86
Total	$	439	$	109	$	1,052	$	155

Summary of Weighted-Average Assumptions Used to Calculate Fair Value of Stock-based Awards Granted

The following weighted-average assumptions were used to calculate the fair value of stock-based awards granted to employees and directors during the periods indicated:

	Three Months Ended						Six Months Ended
	June 30,						June 30,
	2018			2017			2018			2017
Risk-free interest rate		2.93	%		1.79	%		2.66	%		1.79	%
Expected volatility		75.00	%		78.00	%		76.66	%		78.00	%
Expected dividend yield		—			—			—			—
Expected term (in years)		6.08			6.08			5.99			6.08

Summary of Activity under 2012 Equity Incentive Plan

Activity under the 2012 Equity Incentive Plan, as amended, is summarized as follows (in thousands, except per share data):

							Weighted-
	Shares						Average
	Available			Options			Exercise
	for Grant			Outstanding			Price
Balance at December 31, 2017		2,346			4,884		$	0.67
Granted		(2,275	)		2,275		$	4.14
Exercised		—			(416	)	$	0.70
Forfeited		214			(214	)	$	0.50
Balance at June 30, 2018		285			6,529		$	1.88
Options exercisable					3,573		$	1.03
Options vested and expected to vest					6,464		$	1.88

Organization and Business - Additional Information (Details) $ / shares in Units, $ in Thousands			3 Months Ended		6 Months Ended
	Jul. 23, 2018 USD ($) $ / shares shares	Jul. 06, 2018	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)	Jul. 26, 2018 shares	Dec. 31, 2017 USD ($)
Organization and Business [Line Items]
Net loss			$ 9,377	$ 4,692	$ 17,862	$ 9,748
Cash used in operations					17,449	$ 10,021
Accumulated deficit			78,436		78,436			$ 60,574
Cash, cash equivalents and marketable securities			$ 64,100		$ 64,100
Subsequent Event
Organization and Business [Line Items]
Reverse stock split		1-for-1.25
Reverse stock split ratio		0.8
Common Stock \| Subsequent Event
Organization and Business [Line Items]
Proceeds from IPO, net of underwriting discounts and commissions	$ 137,300
Proceeds from private placement	$ 4,500
Initial Public Offering \| Common Stock \| Subsequent Event
Organization and Business [Line Items]
Common stock shares sold \| shares	8,203,332
Common stock offering price per share \| $ / shares	$ 18.00
Convertible preferred stock converted into shares of common stock \| shares	30,971,627						30,971,627
Private Placement \| Common Stock \| Subsequent Event
Organization and Business [Line Items]
Common stock shares sold \| shares	250,000
Common stock offering price per share \| $ / shares	$ 18.00

Summary of Significant Accounting Policies - Reconciliation of Cash, Cash Equivalents and Restricted Cash (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017	Dec. 31, 2016
Supplemental Cash Flow Elements [Abstract]
Cash and cash equivalents	$ 19,295	$ 85,207
Restricted cash in long term assets, deposit for lease facility	802	0
Total cash, cash equivalents and restricted cash	$ 20,097	$ 85,207	$ 3,377	$ 13,416

Summary of Significant Accounting Policies - Additional Information (Details) - USD ($)	3 Months Ended	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Jul. 26, 2018	Jul. 23, 2018	Dec. 31, 2017	Dec. 31, 2016
Summary Of Significant Accounting Policies [Line Items]
Restricted cash	$ 0		$ 0				$ 0
Non-cash interest related to debt facility	$ 25,000	$ 0	$ 50,000
Expected dividend yield		0.00%
Restricted cash in long term assets, deposit for lease facility		$ 802,000				$ 0
ASU 2016-18
Summary Of Significant Accounting Policies [Line Items]
Restricted cash in long term assets, deposit for lease facility						0
Initial Public Offering \| Subsequent Event \| Common Stock
Summary Of Significant Accounting Policies [Line Items]
Convertible preferred stock converted into shares of common stock				30,971,627	30,971,627
Initial Public Offering \| Other Long-Term Assets
Summary Of Significant Accounting Policies [Line Items]
Deferred IPO costs		$ 2,600,000				$ 200,000

Summary of Significant Accounting Policies - Calculation of Basic and Diluted Net Loss per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Numerator:
Net loss	$ (9,377)	$ (4,692)	$ (17,862)	$ (9,748)
Weighted-average number of common shares outstanding:
Weighted-average shares of common stock outstanding, basic and diluted	2,248	1,477	2,137	1,449
Net loss per share, basic and diluted	$ (4.17)	$ (3.18)	$ (8.36)	$ (6.73)

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References + Details

Summary of Significant Accounting Policies - Summary of Potentially Dilutive Securities Excluded from Calculation of Diluted Net Loss per Share (Details) - shares shares in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potentially dilutive securities excluded from calculation of diluted net loss per share due to anti-dilutive effect	37,624	25,747	37,624	25,747
Series A Convertible Preferred Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potentially dilutive securities excluded from calculation of diluted net loss per share due to anti-dilutive effect	20,866	20,866	20,866	20,866
Series B Convertible Preferred Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potentially dilutive securities excluded from calculation of diluted net loss per share due to anti-dilutive effect	10,105		10,105
Options to Purchase Common Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potentially dilutive securities excluded from calculation of diluted net loss per share due to anti-dilutive effect	6,529	4,666	6,529	4,666
Warrants to Purchase Common Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potentially dilutive securities excluded from calculation of diluted net loss per share due to anti-dilutive effect	48	48	48	48
Unvested Restricted Common Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potentially dilutive securities excluded from calculation of diluted net loss per share due to anti-dilutive effect	76	167	76	167

Fair Value Measurements - Summary of Financial Assets Measured at Fair Value on Recurring Basis (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Investments in marketable securities	$ 44,851	$ 0
Fair Value, Measurements, Recurring Basis
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	58,622	82,526
Fair Value, Measurements, Recurring Basis \| Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	13,771	82,526
Fair Value, Measurements, Recurring Basis \| Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	44,851	0
Fair Value, Measurements, Recurring Basis \| Cash Equivalents
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	13,771	82,526
Fair Value, Measurements, Recurring Basis \| Cash Equivalents \| Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	13,771	82,526
Fair Value, Measurements, Recurring Basis \| Cash Equivalents \| Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents		$ 0
Fair Value, Measurements, Recurring Basis \| U.S. Treasuries
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Investments in marketable securities	44,851
Fair Value, Measurements, Recurring Basis \| U.S. Treasuries \| Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Investments in marketable securities	$ 44,851

Fair Value Measurements - Additional Information (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Fair Value Disclosures [Abstract]
Transfers of assets between level 1 to level 2	$ 0	$ 0	$ 0	$ 0
Transfers of assets between level 2 to level 1	0	0	0	0
Transfers of liabilities between level 1 to level 2	0	0	0	0
Transfers of liabilities between level 2 to level 1	0	0	0	0
Transfers of assets into level 3	0	0	0	0
Transfers of assets out of level 3	0	0	0	0
Transfers of liabilities into level 3	0	0	0	0
Transfers of liabilities out of level 3	$ 0	$ 0	$ 0	$ 0

Marketable Securities - Summary of Amortized Cost, Gross Unrealized Holding Gains or Losses, and Fair Value of Marketable Securities (Details) $ in Thousands	Jun. 30, 2018 USD ($)
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost Basis	$ 44,848
Unrealized Gains	4
Unrealized Losses	(1)
Fair Value	44,851
U.S. Treasuries
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost Basis	44,848
Unrealized Gains	4
Unrealized Losses	(1)
Fair Value	$ 44,851

Marketable Securities - Additional Information (Details) - USD ($)	3 Months Ended	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2018	Dec. 31, 2017
Investments Debt And Equity Securities [Abstract]
Other-than-temporary impairments on marketable securities	$ 0	$ 0
Marketable securities			$ 0

Balance Sheet Components and Supplemental Disclosures - Schedule of Property and Equipment, Net (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 4,054	$ 1,004
Less accumulated depreciation	(678)	(559)
Property and equipment, net	3,376	445
Laboratory Equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	1,040	949
Leasehold Improvements
Property Plant And Equipment [Line Items]
Property and equipment, gross	55	55
Construction in Progress
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 2,959	$ 0

Balance Sheet Components and Supplemental Disclosures - Additional Information (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Balance Sheet Related Disclosures [Abstract]
Depreciation and amortization	$ 58,000	$ 62,000	$ 119,000	$ 113,000

Balance Sheet Components and Supplemental Disclosures - Schedule of Accrued Expenses and Other Current Liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Payables And Accruals [Abstract]
Accrued outside professional services	$ 1,214	$ 787
Accrued compensation	1,707	265
Other current liabilities	161	37
Total	$ 3,082	$ 1,089

Commitments and Contingencies - Additional Information (Details)	1 Months Ended		3 Months Ended		6 Months Ended		55 Months Ended	57 Months Ended
	Jan. 31, 2018 USD ($)	Aug. 31, 2015 Provision	Jun. 30, 2018 USD ($) shares	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($) Lease shares	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($) shares	Jun. 30, 2018 USD ($) shares	Dec. 31, 2017 shares	Dec. 31, 2013 shares
Commitments And Contingencies [Line Items]
Number of noncancelable operating leases \| Lease					2
Noncancelable operating leases expiration beginning period					2019-06
Numbe of lease renewal provisions \| Provision		2
Lease term additional extension period		1 year
Net rent expense			$ 300,000	$ 100,000	$ 400,000	$ 200,000
Non-cancelable purchase obligations			$ 0		$ 0		$ 0	$ 0
Common stock, shares issued \| shares			2,529,726		2,529,726		2,529,726	2,529,726	2,114,000
In-Licensing Agreements
Commitments And Contingencies [Line Items]
Milestone expense			$ 0	$ 0	$ 300,000	$ 0
Accrued Royalties			0		0		$ 0	$ 0
Exclusive License Agreement with The Johns Hopkins University
Commitments And Contingencies [Line Items]
Upfront and milestone payments							300,000
Common stock, shares issued \| shares										88,887
Non-exclusive License Agreement with BioWa Inc. and Lonza Sales AG
Commitments And Contingencies [Line Items]
Milestone payments								400,000
Maximum \| Exclusive License Agreement with The Johns Hopkins University
Commitments And Contingencies [Line Items]
Aggregate additional milestone payments							4,000,000
Maximum \| Non-exclusive License Agreement with BioWa Inc. and Lonza Sales AG
Commitments And Contingencies [Line Items]
Aggregate additional milestone payments								41,000,000
Minimum \| Non-exclusive License Agreement with BioWa Inc. and Lonza Sales AG
Commitments And Contingencies [Line Items]
Annual commercial license fees								40,000
Redwood City Lease Agreement
Commitments And Contingencies [Line Items]
Lease term additional extension period	5 years
Lease agreement initiation period	2018-01
Base term of lease	10 years 9 months
Security deposit	$ 800,000
Lease incentive obligations			$ 1,400,000		$ 1,400,000		$ 1,400,000	$ 1,400,000
Redwood City Lease Agreement \| Maximum
Commitments And Contingencies [Line Items]
Tenant improvement allowance	$ 1,400,000

Commitments and Contingencies - Summary of Future Minimum Lease Payments Required Under Operating Leases (Details) $ in Thousands	Jun. 30, 2018 USD ($)
Commitments And Contingencies Disclosure [Abstract]
2018 (remaining 6 months)	$ 210
2019	741
2020	1,239
2021	1,277
2022	1,315
Thereafter	9,429
Total minimum future lease payments	$ 14,211

Convertible Preferred Stock and Stockholders' Deficit - Additional Information (Details) - USD ($)	6 Months Ended
	Jun. 30, 2018	Dec. 31, 2017
Class Of Stock [Line Items]
Total number of shares, authorized to issue	93,714,587
Common stock shares, authorized to issue	55,000,000	55,000,000
Common stock, shares issued	2,529,726	2,114,000
Common stock, shares outstanding	2,529,726	2,114,000
Common stock, dividends declared	$ 0
Preferred Stock
Class Of Stock [Line Items]
Preferred stock shares, authorized to issue	38,714,587
Series A Shares
Class Of Stock [Line Items]
Preferred stock shares, authorized to issue	26,083,081	26,083,000
Series B Shares
Class Of Stock [Line Items]
Preferred stock shares, authorized to issue	12,631,506	12,632,000

Convertible Preferred Stock and Stockholders' Deficit - Summary of Common Stock Shares Reserved for Future Issuance (Details) - shares shares in Thousands	Jun. 30, 2018	Dec. 31, 2017
Class Of Stock [Line Items]
Common stock shares reserved for future issuance	45,577	45,993
Series A Convertible Preferred Stock
Class Of Stock [Line Items]
Common stock shares reserved for future issuance	26,083	26,083
Series B Convertible Preferred Stock
Class Of Stock [Line Items]
Common stock shares reserved for future issuance	12,632	12,632
Stock Options Issued and Outstanding
Class Of Stock [Line Items]
Common stock shares reserved for future issuance	6,529	4,884
Stock Options Available for Future Grant
Class Of Stock [Line Items]
Common stock shares reserved for future issuance	285	2,346
Conversion of Common Stock Warrants
Class Of Stock [Line Items]
Common stock shares reserved for future issuance	48	48

Stock-Based Compensation - Summary of Total Stock-Based Compensation Expense Recognized (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 439	$ 109	$ 1,052	$ 155
Research and Development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	167	42	335	69
General and Administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 272	$ 67	$ 717	$ 86

Stock-Based Compensation - Additional Information (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Tax benefits for stock-based compensation expense recognized	$ 0	$ 0	$ 0	$ 0
Total unrecognized stock-based compensation expense relating to unvested stock options	$ 6,700,000		$ 6,700,000
Performance-Based Vesting
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock options granted	0	0
Market-Based Vesting
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock options granted	0	0
Service-Based Vesting \| Non-Employees
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock options granted	0	0
Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Weighted-average recognition period			3 years

Stock-Based Compensation - Summary of Weighted-Average Assumptions Used to Calculate Fair Value of Stock-based Awards Granted (Details)	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected dividend yield			0.00%
Employees and Directors
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Risk-free interest rate	2.93%	1.79%	2.66%	1.79%
Expected volatility	75.00%	78.00%	76.66%	78.00%
Expected dividend yield	0.00%	0.00%	0.00%	0.00%
Expected term (in years)	6 years 29 days	6 years 29 days	5 years 11 months 26 days	6 years 29 days

Stock-Based Compensation - Summary of Activity under 2012 Equity Incentive Plan (Details) - 2012 Equity Incentive Plan - $ / shares shares in Thousands	6 Months Ended
	Jun. 30, 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares Available for Grant, Beginning balance	2,346
Shares Available for Grant, Granted	(2,275)
Shares Available for Grant, Forfeited	214
Shares Available for Grant, Ending balance	285
Options Outstanding, Beginning balance	4,884
Options Outstanding, Granted	2,275
Options Outstanding, Exercised	(416)
Options Outstanding, forfeited	(214)
Options Outstanding, Ending balance	6,529
Options Outstanding, Options exercisable	3,573
Options Outstanding, Options vested and expected to vest	6,464
Weighted Average Exercise Price, Beginning balance	$ 0.67
Weighted Average Exercise Price, Granted	4.14
Weighted Average Exercise Price, Exercised	0.70
Weighted Average Exercise Price, Forfeited	0.50
Weighted Average Exercise Price, Ending balance	1.88
Weighted Average Exercise Price, Options exercisable	1.03
Weighted Average Exercise Price, Options vested and expected to vest	$ 1.88

Defined Contribution Plan - Additional Information (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
401(K) Plan
Defined Contribution Plan Disclosure [Line Items]
Contributions made by employer	$ 59,000		$ 118,000
Employer contribution matching percentage			4.00%
SIMPLE IRA Plan
Defined Contribution Plan Disclosure [Line Items]
Contributions made by employer		$ 21,000		$ 51,000

Related Party Transactions - Additional Information (Details) - USD ($)	1 Months Ended	6 Months Ended
	Sep. 30, 2014	Jun. 30, 2018	Jun. 30, 2017
Related Party Transaction [Line Items]
Proceeds from fully recourse promissory note		$ 50,000	$ 0
Loan interest rate per annum	2.97%
Loan maturity date	Sep. 19, 2024
Notes repayment date		2018-06
Series A Convertible Preferred Stock
Related Party Transaction [Line Items]
Proceeds from fully recourse promissory note	$ 50,000

Subsequent Events - Additional Information (Details) - Subsequent Event $ / shares in Units, $ in Millions	Jul. 23, 2018 USD ($) $ / shares shares	Jul. 06, 2018	Jul. 26, 2018 shares
Subsequent Event [Line Items]
Reverse stock split		1-for-1.25
Reverse stock split ratio		0.8
Common Stock
Subsequent Event [Line Items]
Proceeds from IPO, net of underwriting discounts and commissions \| $	$ 137.3
Proceeds from private placement \| $	$ 4.5
Initial Public Offering \| Common Stock
Subsequent Event [Line Items]
Convertible preferred stock converted into shares of common stock	30,971,627		30,971,627
Common stock shares sold	8,203,332
Common stock offering price per share \| $ / shares	$ 18.00
Private Placement \| Common Stock
Subsequent Event [Line Items]
Common stock shares sold	250,000
Common stock offering price per share \| $ / shares	$ 18.00