Quarterly Financial Summary (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Interest income	$ 349,731	$ 354,627	$ 346,814	$ 333,970	$ 320,596	$ 304,962	$ 284,047	$ 261,205	$ 1,385,142	$ 1,170,810	$ 946,468
Interest expense	87,852	89,775	80,612	71,984	66,508	57,399	45,877	36,123	330,223	205,907	114,392
Net interest income	261,879	264,852	266,202	261,986	254,088	247,563	238,170	225,082	1,054,919	964,903	832,076
Provision for credit losses	7,826	10,834	24,580	10,624	10,401	11,042	5,043	8,346	53,864	34,832	29,768
Net interest income after provision for credit losses	254,053	254,018	241,622	251,362	243,687	236,521	233,127	216,736	1,001,055	930,071	802,308
Non-interest income, excluding net securities gains (losses)	111,633	114,427	97,294	80,293	77,957	99,840	95,221	86,030
Gains (losses) on investment securities, net	587	710	864	1,364	(2,649)	90	12	(351)	3,525	(2,898)	45
Non-interest expense	249,591	234,554	229,607	214,374	211,333	213,637	206,769	194,349	928,126	826,088	731,817
Income before taxes	116,682	134,601	110,173	118,645	107,662	122,814	121,591	108,066	480,101	460,133	389,997
Income tax expense	30,718	35,480	28,707	29,499	28,005	30,866	32,011	26,085	124,404	116,967	132,315
Net income	85,964	99,121	81,466	89,146	79,657	91,948	89,580	81,981	355,697	343,166	257,682
Preferred stock dividends	2,050	2,050	2,050	2,050	2,050	2,050	2,050	2,050	8,200	8,200	9,778
Net income applicable to common shares	$ 83,914	$ 97,071	$ 79,416	$ 87,096	$ 77,607	$ 89,898	$ 87,530	$ 79,931	$ 347,497	$ 334,966	$ 247,904
Net income per common share:
Basic (usd per share)	$ 1.46	$ 1.71	$ 1.40	$ 1.54	$ 1.38	$ 1.59	$ 1.55	$ 1.42	$ 6.11	$ 5.95	$ 4.53
Diluted (usd per share)	1.44	1.69	1.38	1.52	1.35	1.57	1.53	1.40	6.03	5.86	4.40
Cash dividends declared per common share (usd per share)	$ 0.25	$ 0.25	$ 0.25	$ 0.25	$ 0.19	$ 0.19	$ 0.19	$ 0.19	$ 1.00	$ 0.76	$ 0.56