Quarterly Financial Summary (Unaudited) (Summary Of Quarterly Financial Information) (Details) - USD ($) $ / shares in Units, $ 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
Quarterly Financial Information Disclosure [Abstract]
Interest income	$ 187,487	$ 185,379	$ 175,241	$ 170,357	$ 172,715	$ 170,676	$ 166,550	$ 161,326	$ 718,464	$ 671,267	$ 630,709
Interest expense	20,281	19,839	18,349	18,466	18,996	19,006	17,370	17,320	76,935	72,692	80,082
Net interest income	167,206	165,540	156,892	151,891	153,719	151,670	149,180	144,006	641,529	598,575	550,627
Provision for credit losses	9,059	8,322	9,482	6,079	6,133	5,864	6,660	1,880	32,942	20,537	46,033
Net interest income after provision for credit losses	158,147	157,218	147,410	145,812	147,586	145,806	142,520	142,126	608,587	578,038	504,594
Non-interest income, excluding net securities gains (losses)	65,169	65,051	77,037	64,017	57,639	58,105	54,438	45,562
Net securities gains (losses)	(79)	(98)	(24)	524	18	(153)	(336)	(33)	323	(504)	(3,000)
Non-interest expense	166,829	159,974	154,297	147,318	143,441	138,500	133,591	131,315	628,419	546,847	502,551
Income before taxes	56,408	62,197	70,126	63,035	61,802	65,258	63,031	56,340	251,765	246,431	224,440
Income tax expense	20,896	23,842	26,295	23,983	23,669	25,034	24,490	21,840	95,016	95,033	87,230
Net income	35,512	38,355	43,831	39,052	38,133	40,224	38,541	34,500	156,749	151,398	137,210
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	$ 31,883	$ 34,276	$ 42,251	$ 37,471	$ 36,553	$ 38,643	$ 36,960	$ 32,919	$ 145,880	$ 145,075	$ 128,815
Net income per common share:
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
Cash dividends declared per common share	$ 0.11	$ 0.11	$ 0.11	$ 0.11	$ 0.10	$ 0.10	$ 0.10	$ 0.10	$ 0.44	$ 0.40	$ 0.18