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, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Earnings Per Share [Abstract]
Net income	$ 58,398	$ 57,928	$ 55,792	$ 53,963	$ 53,173	$ 46,788	$ 46,872	$ 48,416	$ 226,082	$ 195,249	$ 159,383
Dividends and accretion of discount on preferred stock									10,238	10,238	40,830
Net income available to common shareholders	$ 55,839	$ 55,369	$ 53,233	$ 51,404	$ 50,612	$ 44,229	$ 44,313	$ 45,857	$ 215,844	$ 185,011	$ 118,553
Weighted average common shares outstanding, basic									132,423	138,495	127,495
Potentially dilutive shares from assumed exercise of securities or other contracts to purchase common stock									778	659	6,731
Weighted average common shares outstanding, diluted									133,201	139,154	134,226
Net income per common share, basic (per share)	$ 0.43	$ 0.42	$ 0.40	$ 0.38	$ 0.37	$ 0.32	$ 0.32	$ 0.33	$ 1.63	$ 1.34	$ 0.93
Net income per common share, diluted (per share)	$ 0.43	$ 0.42	$ 0.40	$ 0.38	$ 0.37	$ 0.32	$ 0.32	$ 0.33	$ 1.62	$ 1.33	$ 0.88