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, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Earnings Per Share [Abstract]
Net income	$ 29,605	$ 98,007	$ 76,003	$ 71,857	$ 68,549	$ 65,245	$ 60,457	$ 52,531	$ 275,474	$ 246,784	$ 226,082
Dividends on preferred stock									10,238	10,238	10,238
Net income available to common shareholders	$ 27,046	$ 95,448	$ 73,444	$ 69,298	$ 65,990	$ 62,686	$ 57,898	$ 49,972	$ 265,236	$ 236,546	$ 215,844
Weighted average common shares outstanding									121,162	124,389	132,423
Potentially dilutive shares from outstanding equity-based awards and Earnout Payments									850	689	778
Weighted average diluted common shares									122,012	125,078	133,201
Net income per common share, basic (in dollars per share)	$ 0.23	$ 0.79	$ 0.60	$ 0.57	$ 0.54	$ 0.51	$ 0.46	$ 0.39	$ 2.19	$ 1.90	$ 1.63
Net income per common share, diluted (in dollars per share)	$ 0.23	$ 0.78	$ 0.60	$ 0.56	$ 0.54	$ 0.51	$ 0.46	$ 0.39	$ 2.17	$ 1.89	$ 1.62