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Stock-Based Compensation - Stock Options (Details) - USD ($)
$ / shares in Units, $ in Thousands
3 Months Ended 12 Months Ended
Mar. 31, 2015
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Number of Shares        
Options outstanding (in shares) 4,400,106 4,400,106 3,632,996 1,817,839
Granted (in shares)   1,902,850 1,600,452 2,323,500
Exercised (in shares)   (481,140) (283,057) (371,743)
Forfeited or expired (in shares)   (548,094) (550,285) (136,600)
Options outstanding (in shares)   5,273,722 4,400,106 3,632,996
Vested and expected to vest (in shares)   5,059,645 3,891,511 3,402,306
Exercisable (in shares)   1,991,141 1,235,710 484,213
Weighted Average Exercise Price        
Options outstanding (in dollars per share) $ 10.59 $ 10.59 $ 7.94 $ 4.10
Granted (in dollars per share)   20.45 16.10 10.53
Exercised (in dollars per share)   10.62 6.11 4.37
Forfeited or expired (in dollars per share)   15.43 11.42 10.49
Options outstanding (in dollars per share)   13.64 10.59 7.94
Vested and expected to vest (in dollars per share)   13.46 10.32 7.88
Exercisable (in dollars per share)   $ 8.70 $ 6.90 $ 4.25
Weighted Average Remaining Contractual Life        
Options outstanding   8 years    
Vested and expected to vest   7 years 11 months 16 days    
Exercisable   7 years 1 month 10 days    
Aggregate Intrinsic Value        
Options outstanding (in dollars)   $ 29,699    
Vested and expected to vest (in dollars)   29,240    
Exercisable (in dollars)   $ 19,128    
Stock options        
Fair value and assumptions used in determining fair value of stock options        
Dividend yield (as a percent)   0.00% 0.00% 0.00%
Expected option term   6 years 3 months 6 years 3 months 6 years 3 months
Weighted-average fair value of stock options granted (in dollars per share)   $ 14.20 $ 11.74 $ 8.16
Stock options | Minimum        
Fair value and assumptions used in determining fair value of stock options        
Volatility (as a percent)   78.00% 83.00% 86.00%
Risk-free interest rate (as a percent)   1.31% 1.46% 0.65%
Stock options | Maximum        
Fair value and assumptions used in determining fair value of stock options        
Volatility (as a percent)   82.00% 86.00% 96.00%
Risk-free interest rate (as a percent)   1.75% 1.83% 1.65%
Performance shares        
Number of Shares        
Options outstanding (in shares)   158,334    
Aggregate Intrinsic Value        
Non-cash compensation expense $ 1,500