Redeemable Convertible Preferred Stock - Summary of Preferred Stock (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Temporary Equity [Line Items]
Preferred stock authorized	0	1,867,886
Preferred stock issued	0	1,574,508
Preferred stock outstanding	0	1,574,508
Preferred share, Carrying Value		$ 50,937
Preferred share, liquidation preference		$ 36,844
Common Stock Issuable Upon Conversion		12,596,064
Series A Redeemable Convertible Preferred Stock [Member]
Temporary Equity [Line Items]
Preferred stock authorized		1,265,100
Preferred stock issued		971,722
Preferred stock outstanding		971,722
Preferred share, Carrying Value		$ 972
Preferred share, liquidation preference		$ 972
Common Stock Issuable Upon Conversion		7,773,776
Series B Redeemable Convertible Preferred Stock [Member]
Temporary Equity [Line Items]
Preferred stock authorized		470,037
Preferred stock issued		470,037
Preferred stock outstanding		470,037
Preferred share, Carrying Value		$ 38,961
Preferred share, liquidation preference		$ 27,972
Common Stock Issuable Upon Conversion		3,760,296
Series B-1 Preferred Stock [Member]
Temporary Equity [Line Items]
Preferred stock authorized		132,749
Preferred stock issued		132,749
Preferred stock outstanding		132,749
Preferred share, Carrying Value		$ 11,004
Preferred share, liquidation preference		$ 7,900
Common Stock Issuable Upon Conversion		1,061,992

Number of shares issued for each share of convertible preferred stock that is converted.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(27))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
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-Section S99
-Paragraph 1
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Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
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-URI http://asc.fasb.org/extlink&oid=109259400&loc=d3e21475-112644

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
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Carrying amount, attributable to parent, of an entity's issued and outstanding stock which is not included within permanent equity. Temporary equity is a security with redemption features that are outside the control of the issuer, is not classified as an asset or liability in conformity with GAAP, and is not mandatorily redeemable. Includes any type of security that is redeemable at a fixed or determinable price or on a fixed or determinable date or dates, is redeemable at the option of the holder, or has conditions for redemption which are not solely within the control of the issuer. Includes stock with a put option held by an ESOP and stock redeemable by a holder only in the event of a change in control of the issuer.

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The aggregate liquidation preference (or restrictions) of stock classified as temporary equity that has a preference in involuntary liquidation considerably in excess of the par or stated value of the shares. The liquidation preference is the difference between the preference in liquidation and the par or stated values of the share. Temporary equity is a security with redemption features that are outside the control of the issuer, is not classified as an asset or liability in conformity with GAAP, and is not mandatorily redeemable. Includes any type of security that is redeemable at a fixed or determinable price or on a fixed or determinable date or dates, is redeemable at the option of the holder, or has conditions for redemption which are not solely within the control of the issuer. If convertible, the issuer does not control the actions or events necessary to issue the maximum number of shares that could be required to be delivered under the conversion option if the holder exercises the option to convert the stock to another class of equity. If the security is a warrant or a rights issue, the warrant or rights issue is considered to be temporary equity if the issuer cannot demonstrate that it would be able to deliver upon the exercise of the option by the holder in all cases. Includes stock with put option held by ESOP and stock redeemable by holder only in the event of a change in control of the issuer.

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