Stock-Based Compensation Expense (Schedule Of Nonvested Performance Unit Awards) (Details) (Performance Unit Awards [Member], USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Performance Unit Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Nonvested, beginning of period	184,196	7,500	1,263,500
Granted	190,700	198,700
Vested	(2,946)	(2,947)	(575,890)
Forfeited	(1,800)	(19,057)	(680,110)
Nonvested, end of period	370,150	184,196	7,500
Weighted Average Grant Date Fair Value, Nonvested, beginning of period	$ 41.88	$ 38.41	$ 30.04
Weighted Average Grant Date Fair Value, Granted	$ 56.14	$ 41.94
Weighted Average Grant Date Fair Value, Vested	$ 38.41	$ 38.41	$ 21.60
Weighted Average Grant Date Fair Value, Forfeited	$ 48.26	$ 41.64	$ 37.10
Weighted Average Grant Date Fair Value, Nonvested, end of period	$ 49.23	$ 41.88	$ 38.41