Earnings Per Share (Computation Of Basic And Diluted Earnings Per Common 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	$ 35,512	$ 38,355	$ 43,831	$ 39,052	$ 38,133	$ 40,224	$ 38,541	$ 34,500	$ 156,749	$ 151,398	$ 137,210
Less: Preferred stock dividends and discount accretion	3,629	4,079	1,580	1,581	1,580	1,581	1,581	1,581	10,869	6,323	8,395
Net income applicable to common shares - Basic	$ 31,883	$ 34,276	$ 42,251	$ 37,471	$ 36,553	$ 38,643	$ 36,960	$ 32,919	145,880	145,075	128,815
Add: Dividends on convertible preferred stock, if dilutive									6,314	6,323	8,325
Net income applicable to common shares - Diluted									$ 152,194	$ 151,398	$ 137,140
Weighted average common shares outstanding									47,838	46,524	38,699
Common stock equivalents									1,029	1,246	7,108
Convertible preferred stock, if dilutive									3,070	3,075	4,141
Total dilutive potential common shares									4,099	4,321	11,249
Weighted average common shares and effect of dilutive potential common shares									51,937	50,845	49,948
Net income per common share - Basic	$ 0.66	$ 0.71	$ 0.89	$ 0.79	$ 0.78	$ 0.83	$ 0.79	$ 0.71	$ 3.05	$ 3.12	$ 3.33
Net income per common share - Diluted	$ 0.64	$ 0.69	$ 0.85	$ 0.76	$ 0.75	$ 0.79	$ 0.76	$ 0.68	$ 2.93	$ 2.98	$ 2.75