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Share-Based Compensation - Restricted Stock Unit and Award Activity (Details)
9 Months Ended
Sep. 30, 2017
$ / shares
shares
Restricted Stock Units  
Number of Units/Awards  
Beginning balance (in shares) | shares 298,357
Granted (in shares) | shares 168,173
Converted into shares of common stock (in shares) | shares (64,750)
Forfeited/expired (in shares) | shares (8,374)
Ending balance (in shares) | shares 393,406
Weighted-average grant-date fair value  
Beginning balance (dollars per share) | $ / shares $ 32.81
Granted (dollars per share) | $ / shares 51.90
Converted into shares of common stock (dollars per share) | $ / shares 29.30
Forfeited (dollars per share) | $ / shares 47.05
Ending balance (dollars per share) | $ / shares $ 41.25
Restricted Stock Awards  
Number of Units/Awards  
Beginning balance (in shares) | shares 365,891
Vested (in shares) | shares (277,821)
Forfeited/expired (in shares) | shares (4,165)
Ending balance (in shares) | shares 83,905
Weighted-average grant-date fair value  
Beginning balance (dollars per share) | $ / shares $ 46.23
Vested (dollars per share) | $ / shares 46.23
Forfeited (dollars per share) | $ / shares 46.23
Ending balance (dollars per share) | $ / shares $ 46.23