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Stock- based Compensation - Stock Option and Restricted Stock Unit Activity (Details) - USD ($)
$ / shares in Units, $ in Thousands
 12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Stock-based Compensation [Abstract]      
Shares, Outstanding, Beginning Balance (in shares) 3,572,116    
Shares, Granted (in shares) 987,680    
Shares, Exercised (in shares) (374,214) (568,906) (1,268,049)
Shares, Forfeited or expired (in shares) (39,518)    
Shares, Outstanding, Ending Balance (in shares) 4,146,064 3,572,116  
Shares, Exercisable (in shares) 1,992,951    
Shares, Vested and expected to vest (in shares) 3,894,148    
Weighted-Average Exercise Price, Outstanding, Beginning Balance (in dollars per share) $ 11.40    
Weighted-Average Exercise Price, Granted (in dollars per share) 31.59    
Weighted-Average Exercise Price, Exercised (in dollars per share) 2.45    
Weighted-Average Exercise Price, Forfeited or expired (in dollars per share) 23.44    
Weighted-Average Exercise Price, Outstanding, Ending Balance (in dollars per share) 16.90 $ 11.40  
Weighted-Average Exercise Price, Exercisable (in dollars per share) 7.94    
Weighted-Average Exercise Price, Vested and expected to vest (in dollars per share) $ 16.50    
Weighted-Average Remaining Contractual Term, Outstanding 7 years 4 months 24 days 7 years 3 months 18 days  
Weighted-Average Remaining Contractual Term, Exercisable 5 years 8 months 12 days    
Weighted-Average Remaining Contractual Term, Vested and expected to vest 7 years 3 months 18 days    
Aggregate Intrinsic Value, Outstanding, Ending Balance $ 59,344    
Aggregate Intrinsic Value, Exercisable 46,012    
Aggregate Intrinsic Value, Vested and expected to vest $ 57,267    
Common stock, shares issued (in shares) 374,214 568,906 1,268,049
Cash proceeds from exercise of stock options $ 911 $ 744 $ 1,100
Weighted-average grant-date fair value of options granted (in dollars per share) $ 20.90 $ 17.41 $ 6.91
Share-based compensation arrangement by share-based payment award, options, exercises in period, intrinsic value $ 10,900 $ 14,500 $ 5,400
Fair value of shares vested 7,300 $ 3,000 $ 500
Unrecognized compensation cost related to non-vested stock-based compensation arrangements $ 30,500    
Unrecognized compensation expense recognition period 4 years