Earnings Per Share (Summary Of Earnings Per Share, Basic And Diluted) (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Summary Of Earnings Per Share, Basic And Diluted [Line Items]
Net income	$ 37,771	$ 40,514	$ 36,715	$ 32,335	$ 17,513	$ 33,398	$ 29,640	$ 27,345	$ 147,335	$ 107,896	$ 89,052
Convertible preferred stock accrued dividends										(1,488)	(15,789)
Earnings attributable to common shareholders for basic earnings per share									147,335	106,408	73,263
Weighted-average shares outstanding									79,477	33,704	32,522
Share-based payment awards classified as participating securities									1,133	1,730	1,280
Denominator for basic earnings per share	81,512	80,819	80,151	79,937	39,612	34,076	33,988	34,011	80,610	35,434	33,802
Dilutive securities									3,044	3,055	3,602
Convertible preferred stock										42,262	41,450
Denominator for diluted earnings per share	84,035	83,649	83,548	83,378	80,931	80,880	80,701	80,489	83,654	80,751	78,854
Basic earnings per share	$ 0.46	$ 0.50	$ 0.46	$ 0.40	$ 0.43	$ 0.85	$ 0.74	$ 0.67	$ 1.83	$ 3.00	$ 2.17
Diluted earnings per share	$ 0.45	$ 0.48	$ 0.44	$ 0.39	$ 0.22	$ 0.41	$ 0.37	$ 0.34	$ 1.76	$ 1.34	$ 1.13
Earnings Per Share, Basic [Member]
Summary Of Earnings Per Share, Basic And Diluted [Line Items]
Net income									147,335	107,896	89,052
Convertible preferred stock accrued dividends										(1,488)	(15,789)
Earnings attributable to common shareholders for basic earnings per share									147,335	106,408	73,263
Earnings Per Share, Diluted [Member]
Summary Of Earnings Per Share, Basic And Diluted [Line Items]
Earnings attributable to common shareholders for basic earnings per share									147,335	106,408	73,263
Effect of convertible preferred stock										1,488	15,789
Net earnings for diluted earnings per share									$ 147,335	$ 107,896	$ 89,052