Earnings Per Share Computation Of Basic And Diluted Earnings Per Common Share (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Earnings Per Share [Line Items]
Net income	$ 44,377	$ 42,302	$ 96,236	$ 85,610
Basic earnings per share	$ 0.77	$ 0.71	$ 1.66	$ 1.43
Diluted earnings per share	$ 0.76	$ 0.71	$ 1.65	$ 1.43
Earnings Per Share, Basic [Member]
Earnings Per Share [Line Items]
Net income	44,377	42,302	96,236	85,610
Income allocated to participating securities	(470)	(417)	(1,016)	(848)
Net income available to common shareholders	43,907	41,885	95,220	84,762
Weighted average common shares outstanding - basic	57,388	59,182	57,455	59,169
Basic earnings per share	$ 0.77	$ 0.71	$ 1.66	$ 1.43
Earnings Per Share, Diluted [Member]
Earnings Per Share [Line Items]
Net income	44,377	42,302	96,236	85,610
Income allocated to participating securities	(493)	(417)	(1,032)	(848)
Weighted average common shares outstanding - basic	57,388	59,182	57,455	59,169
Net income available to common shareholders	$ 43,884	$ 41,885	$ 95,204	$ 84,762
Diluted effect of stock options and PVRSUs	225	36	157	44
Weighted average shares outstanding - diluted	57,613	59,218	57,612	59,213
Diluted earnings per share	$ 0.76	$ 0.71	$ 1.65	$ 1.43