Share-Based Compensation (Schedule Of Unvested Share Activity) (Details) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Share-Based Compensation [Abstract]
Unvested Shares, Nonvested at January 1, 2011	950,097
Unvested shares nonvested, Weighted-Average Grant Date Fair Value at January 1, 2011	$ 29.83
Unvested Shares, Granted	341,876	264,915	273,000
Unvested shares granted, Weighted-Average Grant Date Fair Value	$ 38.81
Unvested Shares, Vested	(386,338)
Unvested shares vested, Weighted-Average Grant Date Fair Value	$ 32.84
Unvested Shares, Forfeited	(292,260)
Unvested shares forfeited, Weighted-Average Grant Date Fair Value	$ 30.03
Unvested Shares, Nonvested at December 31, 2011	613,375	950,097
Unvested shares nonvested, Weighted-Average Grant Date Fair Value at December 31, 2011	$ 32.44	$ 29.83