Stock Benefit Plan (Schedule Of Cash Proceeds Received From Restricted Stock Activity) (Details) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation costs recognized	$ 6,226	$ 4,527	$ 3,549
Fair value of restricted shares vested	$ 5,246	$ 3,447	$ 1,749
Number of restricted shares granted	97,377
Weighted average price of shares granted, per share	$ 62.09	$ 49.35	$ 33.90
Employee Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of restricted shares granted	87,913	108,252	114,078
Employee Awards [Member] | Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of restricted shares granted	87,913	108,252	114,078
Non-Employee Director Awards [Member] | Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of restricted shares granted	9,464	12,760	14,769