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Stockholder's Equity - Nonvested Stock Activity (Details)
3 Months Ended
Mar. 31, 2019
$ / shares
shares
Weighted average grant date fair value  
Granted (in dollars per share) $ 67.16
Restricted stock  
Number of shares  
Share grants outstanding as of December 31, 2018 | shares 574,285
Granted (in shares) | shares 146,830
Vested (in shares) | shares (174,562)
Share grants outstanding as of March 31, 2019 | shares 546,553
Weighted average grant date fair value  
Beginning balance, Weighted average grant date fair value (in dollars per share) $ 49.68
Granted (in dollars per share) 108.93
Vested (in dollars per share) 42.29
Ending balance, Weighted average grant date fair value (in dollars per share) $ 67.16
Options  
Number of shares  
Share grants outstanding as of December 31, 2018 | shares 161,807
Granted (in shares) | shares 0
Vested or exercised (in shares) | shares (44,387)
Share grants outstanding as of March 31, 2019 | shares 117,420
Weighted average grant date fair value  
Share grants outstanding as of December 31, 2018 (in dollars per share) $ 38.08
Granted (in dollars per share) 0.00
Vested or exercised (in dollars per share) 34.87
Share grants outstanding as of March 31, 2019 (in dollars per share) $ 39.73