Stock-Based Compensation - Status of Nonvested Restricted Stock, Stock Grants, Stock Units and Performance Shares (Details) - $ / shares	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Restricted Stock Units, Stock Grants, and Stock Units
Nonvested shares
Balance at the beginning of the period (in shares)	428,287
Granted (in shares)	141,811
Change in performance factor (in shares)	0
Vested (in shares)	(230,881)
Forfeited (in shares)	(3,958)
Balance at the end of the period (in shares)	335,259	428,287
Weighted-Average Grant-Date Fair Value
Balance at the beginning of the period (in dollars per share)	$ 56.69
Granted (in dollars per share)	67.34	$ 64.12	$ 54.89
Change in performance factor (in dollars per share)	0.00
Vested (in dollars per share)	55.07
Forfeited (in dollars per share)	62.86
Balance at the end of the period (in dollars per share)	$ 62.04	$ 56.69
Vested Awards Outstanding at December 31, 2016	174,201
Vested Awards Outstanding at December 31, 2015 (in shares)
Number of nonvested awards to be settled in cash (in shares)	112,554
Performance Shares
Nonvested shares
Balance at the beginning of the period (in shares)	305,832
Granted (in shares)	166,666
Change in performance factor (in shares)	15,573
Vested (in shares)	(171,303)
Forfeited (in shares)	(4,044)
Balance at the end of the period (in shares)	312,724	305,832
Weighted-Average Grant-Date Fair Value
Balance at the beginning of the period (in dollars per share)	$ 58.86
Granted (in dollars per share)	66.60	$ 64.97	$ 54.86
Change in performance factor (in dollars per share)	54.09
Vested (in dollars per share)	54.09
Forfeited (in dollars per share)	62.34
Balance at the end of the period (in dollars per share)	$ 65.32	$ 58.86
Vested Awards Outstanding at December 31, 2016	171,303
Vested Awards Outstanding at December 31, 2015 (in shares)