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Stock Options and Employee Stock Purchase Plan (Restricted Stock and Restricted Stock Unit Award Activity) (Details) - USD ($)
3 Months Ended 6 Months Ended
Jun. 30, 2021
Jun. 30, 2020
Jun. 30, 2021
Jun. 30, 2020
Aggregate Intrinsic Value        
Share-based compensation expense $ 6,251,000 $ 6,530,000 $ 12,363,000 $ 12,843,000
Restricted Stock        
Number of Shares        
Nonvested at beginning of period (in shares)     820,566  
Granted (in shares)     0  
Vested (in shares)     (334,294)  
Canceled (in shares)     (2,067)  
Nonvested at end of period (in shares) 484,205   484,205  
Number of Shares        
Granted (in shares)     0  
Vested (in shares)     (334,294)  
Canceled (in shares)     (2,067)  
Weighted-Average Grant-Date Fair Value        
Nonvested at beginning of period (in usd per share)     $ 62.66  
Granted (in usd per share)     0  
Vested (in usd per share)     64.02  
Canceled (in usd per share)     82.38  
Nonvested at end of period (in usd per share) $ 61.62   $ 61.62  
Restricted Stock Units        
Number of Shares        
Granted (in shares)     163,380  
Vested (in shares)     (100,224)  
Canceled (in shares)     0  
Number of Shares        
Outstanding at beginning of period (in shares)     209,784  
Granted (in shares)     163,380  
Vested (in shares)     (100,224)  
Canceled (in shares)     0  
Outstanding at end of period (in shares) 272,940   272,940  
Vested and expected to vest at end of period (in shares) 182,186   182,186  
Weighted-Average Remaining Contractual Term (in years)        
Outstanding at end of period     3 years 4 months 24 days  
Vested and expected to vest at end of period     2 years 9 months 18 days  
Aggregate Intrinsic Value        
Outstanding at end of period $ 37,542,897   $ 37,542,897  
Vested and expected to vest at end of period 25,059,725   25,059,725  
Restricted Stock And Restricted Stock Unit (RSU)        
Aggregate Intrinsic Value        
Share-based compensation expense $ 5,400,000 $ 5,700,000 $ 10,700,000 $ 11,300,000