Stockholders' Equity - ESPP Activity (Details) - ESPP - shares	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Beginning Balance, Equity securities available (shares)	228,279	246,039	0
Plus: Registration of 2016 ESPP (shares)			250,000
Less: common stock purchased by eligible employees (shares)	(20,120)	(17,760)	(3,961)
Ending Balance, Equity securities available (shares)	208,159	228,279	246,039

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.

No definition available.

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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.

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- Definition

Gross number of share options (or share units) granted during the period.

+ References

No definition available.

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- Definition

Number of share options (or share units) exercised during the current period.

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