Common Stock (Basic And Diluted Earnings Per Share) (Details) (USD $) In Thousands, except Share data	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Class of Stock Disclosures [Abstract]
Basic number of common shares outstanding	41,307,632	42,921,044	41,819,428	43,370,487	41,969,628	43,523,270
Dilutive effect of unvested performance awards	231,230	117,796	198,578	76,960	192,994	85,595
Dilutive effect of stock options	26,111	64,858	33,301	57,987	44,390	63,459
Diluted number of common shares outstanding	41,564,973	43,103,698	42,051,307	43,505,434	42,207,012	43,672,324
Net income	$ 58,321	$ 60,182	$ 98,086	$ 93,138	$ 105,551	$ 101,099
Income allocated to participating restricted stock	(275)	(260)	(447)	(383)	(461)	(405)
Net income available to common shareholders	58,046	59,922	97,639	92,755	105,090	100,694
Income reallocated to participating restricted stock	(273)	(259)	(445)	(382)	(459)	(404)
Net income available to common shareholders	$ 58,048	$ 59,923	$ 97,641	$ 92,756	$ 105,092	$ 100,695
Distributed earnings per share basic	$ 0.22	$ 0.00	$ 0.44	$ 0.00	$ 0.44	$ 0.00
Undistributed earnings per share basic	$ 1.19	$ 1.40	$ 1.89	$ 2.14	$ 2.06	$ 2.31
Basic net income per common share	$ 1.41	$ 1.40	$ 2.33	$ 2.14	$ 2.50	$ 2.31
Distributed earnings per share diluted	$ 0.22	$ 0.00	$ 0.44	$ 0.00	$ 0.44	$ 0.00
Undistributed earnings per share diluted	$ 1.18	$ 1.39	$ 1.88	$ 2.13	$ 2.05	$ 2.31
Diluted net income per common share	$ 1.40	$ 1.39	$ 2.32	$ 2.13	$ 2.49	$ 2.31