Stockholders' Equity - Summary of Stock-based Compensation Expense Recognized (Details) - USD ($) $ in Thousands |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2017 |
Dec. 31, 2016 |
Dec. 31, 2015 |
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| Stock-based compensation expense by type of award: | |||
| Stock-based compensation expense | $ 9,640 | $ 7,294 | $ 3,640 |
| Stock Option Plan Awards | |||
| Stock-based compensation expense by type of award: | |||
| Stock-based compensation expense | 7,652 | 6,850 | 3,280 |
| Restricted stock units and restricted stock awards | |||
| Stock-based compensation expense by type of award: | |||
| Stock-based compensation expense | 1,447 | ||
| Employee Stock Purchase Plan | |||
| Stock-based compensation expense by type of award: | |||
| Stock-based compensation expense | $ 541 | $ 444 | $ 360 |
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- Definition Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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