Annual report pursuant to Section 13 and 15(d)

Stockholders' Equity - Summary of Stock-based Compensation Expense Recognized (Details)

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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
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