Stock-Based Compensation (Summary of Restricted Stock Activity and Unvested Shares) (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Stock Options [Member]
Restricted Stock, Granted, Weighted Average Grant Date Fair Value	$ 16.91	$ 18.17	$ 19.40
Restricted Stock [Member]
Restricted Stock, Unvested shares at January 1, Number of Shares	1,019,737	834,058	794,529
Restricted Stock, Granted, Number of Shares	537,244	532,754	390,415
Restricted Stock, Vested, Number of Shares	(344,164)	(294,358)	(319,894)
Restricted Stock, Forfeited, Number of Shares	(95,302)	(52,717)	(30,992)
Restricted Stock, Unvested shares at December 31, Number of Shares	1,117,515	1,019,737	834,058
Restricted Stock, Unvested shares at January 1, Weighted Average Grant Date Fair Value	$ 36.71	$ 36.24	$ 33.70
Restricted Stock, Granted, Weighted Average Grant Date Fair Value	$ 34.39	$ 36.41	$ 36.46
Restricted Stock, Vested, Weighted Average Grant Date Fair Value	$ 36.50	$ 34.90	$ 30.45
Restricted Stock, Forfeited, Weighted Average Grant Date Fair Value	$ 36.97	$ 36.45	$ 33.54
Restricted Stock, Unvested shares at December 31, Weighted Average Grant Date Fair Value	$ 35.64	$ 36.71	$ 36.24