Quarterly Financial Summary (Unaudited) (Summary Of Quarterly Financial Information) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Quarterly Financial Information Disclosure [Abstract]
Interest income	$ 320,596	$ 304,962	$ 284,047	$ 261,205	$ 251,840	$ 247,688	$ 231,181	$ 215,759	$ 1,170,810	$ 946,468	$ 812,457
Interest expense	66,508	57,399	45,877	36,123	32,741	31,700	26,772	23,179	205,907	114,392	90,264
Net interest income	254,088	247,563	238,170	225,082	219,099	215,988	204,409	192,580	964,903	832,076	722,193
Provision for credit losses	10,401	11,042	5,043	8,346	7,772	7,896	8,891	5,209	34,832	29,768	34,084
Net interest income after provision for credit losses	243,687	236,521	233,127	216,736	211,327	208,092	195,518	187,371	930,071	802,308	688,109
Non-interest income, excluding net securities gains (losses)	77,957	99,840	95,221	86,030	81,024	79,692	89,925	68,820
(Losses) gains on investment securities, net	(2,649)	90	12	(351)	14	39	47	(55)	(2,898)	45	7,645
Non-interest expense	211,333	213,637	206,769	194,349	196,580	183,575	183,544	168,118	826,088	731,817	681,685
Income before taxes	107,662	122,814	121,591	108,066	95,785	104,248	101,946	88,018	460,133	389,997	331,854
Income tax expense	28,005	30,866	32,011	26,085	27,004	38,622	37,049	29,640	116,967	132,315	124,979
Net income	79,657	91,948	89,580	81,981	68,781	65,626	64,897	58,378	343,166	257,682	206,875
Preferred stock dividends	2,050	2,050	2,050	2,050	2,050	2,050	2,050	3,628	8,200	9,778	14,513
Net income applicable to common shares	$ 77,607	$ 89,898	$ 87,530	$ 79,931	$ 66,731	$ 63,576	$ 62,847	$ 54,750	$ 334,966	$ 247,904	$ 192,362
Net income per common share:
Basic (usd per share)	$ 1.38	$ 1.59	$ 1.55	$ 1.42	$ 1.19	$ 1.14	$ 1.15	$ 1.05	$ 5.95	$ 4.53	$ 3.83
Diluted (usd per share)	1.35	1.57	1.53	1.40	1.17	1.12	1.11	1.00	5.86	4.40	3.66
Cash dividends declared per common share (in usd per share)	$ 0.19	$ 0.19	$ 0.19	$ 0.19	$ 0.14	$ 0.14	$ 0.14	$ 0.14	$ 0.76	$ 0.56	$ 0.48