Quarterly Financial Summary (Unaudited) (Summary Of Quarterly Financial Information) (Details) - USD ($) $ / shares in Units, $ 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
Quarterly Financial Information Disclosure [Abstract]
Interest income	$ 215,013	$ 208,149	$ 197,064	$ 192,231	$ 187,487	$ 185,379	$ 175,241	$ 170,357	$ 812,457	$ 718,464	$ 671,267
Interest expense	24,235	23,513	21,794	20,722	20,281	19,839	18,349	18,466	90,264	76,935	72,692
Net interest income	190,778	184,636	175,270	171,509	167,206	165,540	156,892	151,891	722,193	641,529	598,575
Provision for credit losses	7,350	9,571	9,129	8,034	9,059	8,322	9,482	6,079	34,084	32,942	20,537
Net interest income after provision for credit losses	183,428	175,065	166,141	163,475	158,147	157,218	147,410	145,812	688,109	608,587	578,038
Non-interest income, excluding net securities gains (losses)	83,700	83,299	83,359	67,427	65,169	65,051	77,037	64,017
Net securities gains (losses)	1,575	3,305	1,440	1,325	(79)	(98)	(24)	524	7,645	323	(504)
Non-interest expense	180,371	176,615	170,969	153,730	166,829	159,974	154,297	147,318	681,685	628,419	546,847
Income before taxes	88,332	85,054	79,971	78,497	56,408	62,197	70,126	63,035	331,854	251,765	246,431
Income tax expense	33,724	31,939	29,930	29,386	20,896	23,842	26,295	23,983	124,979	95,016	95,033
Net income	54,608	53,115	50,041	49,111	35,512	38,355	43,831	39,052	206,875	156,749	151,398
Preferred stock dividends	3,629	3,628	3,628	3,628	3,629	4,079	1,580	1,581	14,513	10,869	6,323
Net income applicable to common shares	$ 50,979	$ 49,487	$ 46,413	$ 45,483	$ 31,883	$ 34,276	$ 42,251	$ 37,471	$ 192,362	$ 145,880	$ 145,075
Net income per common share:
Net income per common share - Basic (usd per share)	$ 0.98	$ 0.96	$ 0.94	$ 0.94	$ 0.66	$ 0.71	$ 0.89	$ 0.79	$ 3.83	$ 3.05	$ 3.12
Net income per common share - Diluted (usd per share)	0.94	0.92	0.90	0.90	0.64	0.69	0.85	0.76	3.66	2.93	2.98
Cash dividends declared per common share (usd dollars per share)	$ 0.12	$ 0.12	$ 0.12	$ 0.12	$ 0.11	$ 0.11	$ 0.11	$ 0.11	$ 0.48	$ 0.44	$ 0.40