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Share-Based Compensation - Restricted Stock Awards and Performance Share Awards Activity (Details) - $ / shares
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
RSA      
Restricted Stock Awards and Units      
Granted (in shares) 12,488 25,088 9,194
Restricted Stock      
Restricted Stock Awards and Units      
Outstanding at beginning of year (in shares) 622,814 566,447 691,621
Granted (in shares) 199,629 389,193 185,782
Released (in shares) (165,846) (275,229) (253,801)
Forfeited (in shares) (27,955) (57,597) (57,155)
Outstanding at end of year (in shares) 628,642 622,814 566,447
Weighted-Average Grant Date Fair Value      
Outstanding at beginning of year (in USD per share) $ 70.19 $ 77.68 $ 60.06
Granted (in USD per share) 98.90 51.93 107.17
Released (in USD per share 75.90 59.39 51.95
Forfeited (in USD per share) 72.81 70.50 75.11
Outstanding at end of year (in USD per share) $ 77.70 $ 70.19 $ 77.68
Performance Share Awards      
Restricted Stock Awards and Units      
Outstanding at beginning of year (in shares) 379,226 332,630 374,180
Granted (in shares) 79,423 172,024 106,411
Released (in shares) (2,029) (111,325) (120,000)
Forfeited (in shares) (190,873) (14,103) (27,961)
Outstanding at end of year (in shares) 265,747 379,226 332,630
Weighted-Average Grant Date Fair Value      
Outstanding at beginning of year (in USD per share) $ 70.14 $ 73.40 $ 61.53
Granted (in USD per share) 98.97 51.01 75.77
Released (in USD per share 62.70 46.58 38.67
Forfeited (in USD per share) 73.09 75.73 73.45
Outstanding at end of year (in USD per share) $ 77.04 $ 70.14 $ 73.40
Maximum | RSA      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Award vesting period 3 years