Stock-Based Compensation (Schedule Of Non-Vested Restricted Stock Award Activity And Changes) (Details) (USD $)	3 Months Ended
	Mar. 31, 2012
Stock-Based Compensation [Abstract]
Number of Shares, Non-vested at December 31, 2011	582,013
Number of Shares, Granted	68,715
Number of Shares, Vested	(298,151)
Number of Shares, Forfeited	(2,060)
Number of Shares, Non-vested at March 31, 2012	350,517
Weighted Average Grant Date Fair Value, Non-vested at December 31, 2011	$ 23.43
Weighted Average Grant Date Fair Value, Granted	$ 60.11
Weighted Average Grant Date Fair Value, Vested	$ 17.51
Weighted Average Grant Date Fair Value, Forfeited	$ 27.64
Weighted Average Grant Date Fair Value, Non-vested at March 31, 2012	$ 35.64