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Stockholders' Equity - Share Activity (Details)
3 Months Ended
Mar. 31, 2018
$ / shares
shares
Number of Shares  
Beginning Balance (shares) 578,394
Granted (shares) 510,253
Vested (shares) (195,972)
Forfeited (shares) (151,965)
Ending Balance (shares) 740,710
Weighted Average Grant Date Fair Value  
Begining Balance (usd per share) | $ / shares $ 58.35
Granted (usd per share) | $ / shares 72.46
Vested (usd per share) | $ / shares 55.16
Forfeited (usd per share) | $ / shares 62.99
Ending Balance (usd per share) | $ / shares $ 67.96
Restricted Stock Awards  
Number of Shares  
Beginning Balance (shares) 401,804
Granted (shares) 321,798
Vested (shares) (163,043)
Forfeited (shares) (59,931)
Ending Balance (shares) 500,628
Performance Stock Awards  
Number of Shares  
Beginning Balance (shares) 84,762
Granted (shares) 0
Vested (shares) (32,929)
Forfeited (shares) (44,384)
Ending Balance (shares) 7,449
Performance Stock Units  
Number of Shares  
Beginning Balance (shares) 91,828
Granted (shares) 188,455
Vested (shares) 0
Forfeited (shares) (47,650)
Ending Balance (shares) 232,633