Earnings Per Share Computation Of Basic And Diluted Earnings Per Common Share (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Net income	$ 110,396	$ 107,441	$ 98,250
Weighted average common shares outstanding - basic	58,862	58,953	59,514
Basic earnings per share	$ 1.86	$ 1.80	$ 1.64
Diluted effect of stock options and PVRSUs	72	88	156
Weighted average common shares outstanding - diluted	58,934	59,041	59,670
Diluted earnings per share	$ 1.85	$ 1.80	$ 1.63
Earnings Per Share, Basic
Net income	110,396	107,441	98,250
Income allocated to participating securities	(1,099)	(1,109)	(906)
Net income available to common shareholders	109,297	106,332	97,344
Basic earnings per share	$ 1.86	$ 1.80	$ 1.64
Earnings Per Share, Diluted
Net income	110,396	107,441	98,250
Income allocated to participating securities	(1,098)	(1,108)	(905)
Net income available to common shareholders	$ 109,298	$ 106,333	$ 97,345
Diluted earnings per share	$ 1.85	$ 1.80	$ 1.63