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Stock-Based Compensation - Summary of Activity Under Restricted and Performance Stock Plans (Details) - $ / shares
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Restricted stock      
Shares      
Outstanding at beginning of period (in shares) 184,885 191,397 160,216
Granted (in shares) 225,954 86,984 60,850
Performance share awards converted to restricted stock (in shares)     (45,844)
Vested (in shares) (101,644) (93,496) (62,628)
Forfeited (in shares)     (12,885)
Outstanding at end of period (in shares) 309,195 184,885 191,397
Weighted-Average Grant-Date Fair Value      
Outstanding at beginning of the period (in dollars per share) $ 54.63 $ 57.12 $ 59.14
Granted (in dollars per share) 32.79 52.21 51.85
Performance share awards converted to restricted stock (in dollars per share)     60.28
Vested (in dollars per share) 55.58 57.48 59.30
Forfeited (in dollars per share)     58.06
Outstanding at end of the period in dollars per share) $ 38.36 $ 54.63 $ 57.12
Performance shares      
Shares      
Outstanding at beginning of period (in shares) 77,594 49,471 46,541
Granted (in shares) 189,325 77,594 52,364
Performance share awards converted to restricted stock (in shares) 0 0 (45,844)
Forfeited (in shares) (77,594) (49,471) (3,590)
Outstanding at end of period (in shares) 189,325 77,594 49,471
Weighted-Average Grant-Date Fair Value      
Outstanding at beginning of the period (in dollars per share) $ 49.64 $ 49.29 $ 60.28
Granted (in dollars per share) 29.94 49.64 49.29
Performance share awards converted to restricted stock (in dollars per share) 0.00 0.00 60.28
Forfeited (in dollars per share) 49.64 49.29 51.42
Outstanding at end of the period in dollars per share) $ 29.94 $ 49.64 $ 49.29