Stock-Based Compensation - 2015 Equity Incentive Plan (Details) - shares	12 Months Ended
Dec. 31, 2018	Jun. 30, 2015
2015 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common shares reserved for issuance (in shares)		4,700,000
Common shares reserved for issuance, annual increase period (not more than) (years)	10 years
Common shares reserved for issuance, percentage of annual increase (percent)	5.00%
Shares available to be issued (shares)	7,455,706
2009 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available to be issued (shares)	0

Common Stock, Capital Shares Reserved for Future Issuance, Annual Increase, Maximum Term

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- Definition

Common Stock, Capital Shares Reserved for Future Issuance, Annual Percentage Increase

+ References

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- Definition

Aggregate number of common shares reserved for future issuance.

+ References

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 210.5-02.29)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

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- Definition

The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

+ 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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