Net Loss per Share Attributable to Common Stockholders - Additional Information (Details) - 2015 ESPP - USD ($)	6 Months Ended
Jun. 30, 2018	Jun. 30, 2017
Earnings Per Share [Line Items]
ESPP contributions from plan participants	$ 213,000	$ 130,000
Contributions converted shares under benefit plan	4,952	11,216
Percentage of stock price at the beginning of offering period	85.00%	85.00%

Earnings per share.

No definition available.

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- Definition

Amount of contributions received by defined benefit plan from participant which increase benefit obligation.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (a)(3)
-URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e1928-114920

+ Details

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- Definition

Discount rate from fair value on offering date that participants pay for shares.

+ References

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

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- Definition

Number of shares issued during the period to an employee benefit plan, such as a defined contribution or defined benefit plan.

+ References

No definition available.

+ Details

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