Stock-Based Compensation (Summary Of The Status Of Nonvested Share Awards) (Details) (USD $)	3 Months Ended
	Mar. 31, 2012
Stock-Based Compensation [Abstract]
Nonvested, Shares, Beginning Balance	653,782
Granted, Shares	207,985
Vested, Shares	(30,626)
Forfeited, Shares	(514)
Nonvested, Shares, Ending Balance	830,627
Nonvested, Weighted Average Grant Date Fair Value, Beginning Balance	$ 35.48
Granted , Weighted Average Grant Date Fair Value	$ 38.47
Vested , Weighted Average Grant Date Fair Value	$ 38.79
Forfeited , Weighted Average Grant Date Fair Value	$ 36.23
Nonvested , Weighted Average Grant Date Fair Value, Ending Balance	$ 36.11