Stock-Based Compensation - Status of Nonvested Restricted Stock, Stock Grants, Stock Units and Performance Shares (Details) - $ / shares	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Restricted Stock Units, Stock Grants, and Stock Units
Nonvested shares
Balance at the beginning of the period (in shares)	480,933
Granted (in shares)	152,651
Change in performance factor (in shares)	0
Vested (in shares)	(198,424)
Forfeited (in shares)	(6,873)
Balance at the end of the period (in shares)	428,287	480,933
Weighted-Average Grant-Date Fair Value
Balance at the beginning of the period (in dollars per share)	$ 51.27
Granted (in dollars per share)	$ 64.12	$ 54.89	$ 55.14
Change in performance factor (in dollars per share)	0.00
Vested (in dollars per share)	$ 49.20
Forfeited (in dollars per share)	56.78
Balance at the end of the period (in dollars per share)	$ 56.69	$ 51.27
Vested Awards Outstanding at December 31, 2015	106,712
Vested Awards Outstanding at December 31, 2015 (in shares)
Number of nonvested awards to be settled in cash (in shares)		127,634
Number of nonvested awards to be settled in shares (in shares)		353,299
Performance Shares
Nonvested shares
Balance at the beginning of the period (in shares)	324,230
Granted (in shares)	151,430
Change in performance factor (in shares)	40,496
Vested (in shares)	(202,480)
Forfeited (in shares)	(7,844)
Balance at the end of the period (in shares)	305,832	324,230
Weighted-Average Grant-Date Fair Value
Balance at the beginning of the period (in dollars per share)	$ 54.92
Granted (in dollars per share)	$ 64.97	$ 54.86	$ 55.45
Change in performance factor (in dollars per share)	54.98
Vested (in dollars per share)	$ 54.98
Forfeited (in dollars per share)	57.89
Balance at the end of the period (in dollars per share)	$ 59.78	$ 54.92
Vested Awards Outstanding at December 31, 2015	202,480
Vested Awards Outstanding at December 31, 2015 (in shares)