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Employee Benefit Plans and Stock-based Compensation - Options (Details) - Options - USD ($)
$ / shares in Units, $ in Thousands
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Number of options outstanding [Roll Forward]        
Options outstanding, beginning of period (in shares) 3,294,000 3,779,000 3,198,000  
Granted (in shares) 184,000 624,000 866,000  
Exercised (in shares) (762,000) (555,000) (119,000)  
Canceled and expired (in shares) (50,000) (554,000) (166,000)  
Options outstanding, end of period (in shares) 2,666,000 3,294,000 3,779,000 3,198,000
Options vested and unvested options expected to vest, net of forfeitures, end of period (in shares) 2,629,000      
Options exercisable, end of period (in shares) 1,580,000      
Weighted average exercise price [Roll Forward]        
Options outstanding, beginning of period (in dollars per share) $ 3.38 $ 2.97 $ 3.12  
Granted (in dollars per share) 8.99 4.92 2.19  
Exercised (in dollars per share) 3.25 2.41 1.38  
Canceled and expired (in dollars per share) 3.47 3.26 3.03  
Options outstanding, end of period (in dollars per share) 3.81 3.38 2.97 $ 3.12
Options vested as of March 31, 2015 and unvested options expected to vest, net of forfeitures (in dollars per share) 3.78      
Options exercisable, end of period (in dollars per share) 3.37      
Weighted-average grant date fair value of stock options granted (in dollars per share) $ 3.67 $ 1.85 $ 0.88  
Weighted average Remaining Contractual Life [Abstract]        
Options outstanding 6 years 10 months 13 days 7 years 2 months 23 days 6 years 3 months 4 days 6 years 11 months 12 days
Options vested and unvested options expected to vest, net of forfeitures, end of period 6 years 10 months 2 days      
Option exercisable, end of period 5 years 9 months 29 days      
Aggregate Intrinsic Value [Abstract]        
Options outstanding, beginning of period $ 5,301 $ 764 $ 1,247  
Options outstanding, end of period 13,149 $ 5,301 $ 764 $ 1,247
Options vested and expected to vest, end of period 13,031      
Options exercisable, end of period $ 8,419