Stock-Based Compensation - Equity Incentive Plans (Details) - shares		6 Months Ended
Jul. 26, 2013	Jun. 30, 2018	Dec. 31, 2017
Class of Stock
Common stock options outstanding		2,955,075	2,675,184
Options outstanding under earlier plans		511,093
Grant of inducement stock option		393,750
2013 Stock Incentive Plan
Class of Stock
Maximum number of additional common shares.	868,372
Common stock options outstanding		2,050,232
Common shares available for grant	3,153,057	1,308,485

Maximum number of additional common shares.

No definition available.

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- Definition

Options outstanding under earlier plans.

+ References

No definition available.

+ Details

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- Definition

Shares granted as inducement grants non-statutory stock options.

+ References

No definition available.

+ Details

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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

No definition available.

+ Details

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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

+ Details

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- Definition

Number of options outstanding, including both vested and non-vested options.

+ 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

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(i)-(ii)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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