Stock-Based Compensation (Schedule Of Non-Vested Restricted Stock Award Activity And Changes) (USD $)	12 Months Ended
	Dec. 31, 2011
Stock-Based Compensation [Abstract]
Number of Shares, Non-vested at December 31, 2010	654,241
Number of Shares, Granted	78,828
Number of Shares, Vested	(143,121)
Number of Shares, Forfeited	(7,935)
Number of Shares, Non-vested at December 31, 2011	582,013
Weighted Average Grant Date Fair Value, Non-vested at December 31, 2010	$ 19.97
Weighted Average Grant Date Fair Value, Granted	$ 45.03
Weighted Average Grant Date Fair Value, Vested	$ 19.64
Weighted Average Grant Date Fair Value, Forfeited	$ 20.48
Weighted Average Grant Date Fair Value, Non-vested at December 31, 2011	$ 23.43