Stockholders Deficit - Summary of Material Factors Incorporated in Black-Scholes Model in Estimating Fair Value of Options Granted (Parenthetical) (Details)	12 Months Ended
Dec. 31, 2018 USD ($)
Class Of Stock [Line Items]
Expected dividend assumed value	$ 0
2014 Employee Stock Purchase Plan
Class Of Stock [Line Items]
Expected dividend assumed value	$ 0

The estimated amount of dividends to be paid to holders of the underlying shares (expected dividends) over the option's term. Dividends are taken into account because payment of dividends to shareholders reduces the fair value of the underlying shares, and option holders generally do not receive dividends.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (f)(2)(iii)
-URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration