Stock-Based Compensation Stock-Based Compensation - Status of Restricted Stock Units and Stock Grants (Details) (Restricted stock units and stock grants, USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Restricted stock units and stock grants
Nonvested shares
Balance at the beginning of the period (in shares)	397,976
Granted (in shares)	130,273
Vested (in shares)	(161,283)
Forfeited (in shares)	(13,067)
Balance at the end of the period (in shares)	353,899	397,976
Weighted-Average Grant-Date Fair Value
Balance at the beginning of the period (in dollars per share)	$ 47.74
Granted (in dollars per share)	$ 54.91	$ 55.21	$ 49.31
Vested (in dollars per share)	$ 45.55
Forfeited (in dollars per share)	$ 51.53
Balance at the end of the period (in dollars per share)	$ 51.23	$ 47.74