Net Income Per Common Share (Schedule Of Basic And Diluted Earnings Per Share) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Earnings Per Share [Abstract]
Net income	$ 68,549	$ 65,245	$ 60,457	$ 52,531	$ 58,398	$ 57,928	$ 55,792	$ 53,963	$ 246,784	$ 226,082	$ 195,249
Dividends on preferred stock									10,238	10,238	10,238
Net income available to common shareholders	$ 65,990	$ 62,686	$ 57,898	$ 49,972	$ 55,839	$ 55,369	$ 53,233	$ 51,404	$ 236,546	$ 215,844	$ 185,011
Weighted average common shares outstanding									124,389	132,423	138,495
Potentially dilutive shares from outstanding equity-based awards									689	778	659
Weighted average diluted common shares									125,078	133,201	139,154
Net income per common share, basic (per share)	$ 0.54	$ 0.51	$ 0.46	$ 0.39	$ 0.43	$ 0.42	$ 0.40	$ 0.38	$ 1.90	$ 1.63	$ 1.34
Net income per common share, diluted (per share)	$ 0.54	$ 0.51	$ 0.46	$ 0.39	$ 0.43	$ 0.42	$ 0.40	$ 0.38	$ 1.89	$ 1.62	$ 1.33