Share-Based Compensation (Summary of the Corporation's Restricted Stock Activity and Related Information) (Details) (Restricted Stock, USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2012
Restricted Stock
Non-vested balance at January 1, 2012	2,033
Granted (Shares)	1,070
Forfeited (Shares)	(53)
Vested (Shares)	(467)
Non-vested balance at December 31, 2012	2,583
Non-vested balance at January 1, 2012 (Weighted Average Grant-Date Fair Value)	$ 32.97
Granted (Weighted Average Grant-Date Fair Value)	$ 29.61
Forfeited (Weighted Average Grant-Date Fair Value)	$ 30.16
Vested (Weighted Average Grant-Date Fair Value)	$ 34.89
Non-vested balance at December 31, 2012 (Weighted Average Grant-Date Fair Value)	$ 31.31