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Stock-Based Compensation - Stock Options and Employee Stock Purchase Plan - Additional Information (Details) - Employee Stock Purchase Plan - USD ($)
$ in Millions
3 Months Ended
Mar. 31, 2016
Mar. 31, 2015
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]    
Number of shares purchased 1,236,759 1,183,426
Number of shares approved and available under the Employee Stock Purchase Plan 7,927,722  
Unamortized stock based compensation expense expected to be recognized $ 11.5  
Unamortized stock based compensation expense recognition period 3 months