Net Loss per Share Attributable to Common Stockholders - Additional Information (Details) - 2015 ESPP - USD ($)	3 Months Ended
Mar. 31, 2018	Mar. 31, 2017
Earnings Per Share [Line Items]
ESPP contributions from plan participants	$ 367,000	$ 338,400
Contributions converted shares under benefit plan	11,066	29,381
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://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (a)(3)
-URI http://asc.fasb.org/extlink&oid=82843861&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://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

+ Details

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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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- Details

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