Share-Based Compensation (Schedule Of Share And Dividend Equivalent Share Award Activity) (Details) (USD $)	3 Months Ended
	Mar. 31, 2012		Mar. 31, 2011
Share-Based Compensation [Abstract]
Number of share equivalents, Beginning Balance	232,921		119,194
Dividend equivalents, Beginning Balance	8,942		3,741
Total share equivalents, Beginning Balance	241,863		122,935
Value of share equivalents, Beginning Balance	$ 11,924,000	[1]	$ 7,269,000	[1]
Number of share equivalents, Granted	97,927		111,027
Dividend equivalents, Granted	2,109		1,315
Total share equivalents, Granted	100,036		112,342
Value of share equivalents, Granted	5,349,000	[1]	6,755,000	[1]
Number of share equivalents, Forfeited share equivalents	(2,191)
Dividend equivalents, Forfeited share equivalents	(95)
Total share equivalents, Forfeited share equivalents	(2,286)
Value of share equivalents, Forfeited share equivalents	(122,000)	[1]		[1]
Number of share equivalents, Vested share equivalents	(5,483)		(1,350)
Dividend equivalents, Vested share equivalents	(350)		(77)
Total share equivalents, Vested share equivalents	(5,833)		(1,427)
Value of share equivalents, Vested share equivalents	(309,000)	[1]	(82,000)	[1]
Number of share equivalents, Ending Balance	323,174		228,871
Dividend equivalents, Ending Balance	10,606		4,979
Total share equivalents, Ending Balance	333,780		233,850
Value of share equivalents, Ending Balance	$ 17,847,000	[1]	$ 14,061,000	[1]
Market price of Company's stock	$ 53.47		$ 60.13

[1] Except for vested share payments, which are based on the cash paid at the time of vesting, the value of share equivalents is calculated based on the market price of the Company's stock at the end of the respective periods. The market price of the Company's stock was $53.47 and $60.13 on March 31, 2012 and 2011, respectively.