Selected Quarterly Consolidated Financial Information (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Selected Quarterly Financial Information [Abstract]
Interest income	$ 236,065	$ 239,239	$ 252,275	$ 274,470	$ 282,000	$ 294,136	$ 292,257	$ 286,190	$ 1,002,049	$ 1,154,583	$ 1,055,167
Interest expense	19,136	19,983	27,868	43,669	50,750	53,597	50,470	44,639	110,656	199,456	148,486
Net interest income	216,929	219,256	224,407	230,801	231,250	240,539	241,787	241,551	891,393	955,127	906,681
Provision for credit losses	(1,000)	22,750	40,000	76,000	6,000	11,300	11,900	8,600	137,750	37,800	42,000
Non-interest income	76,763	75,060	60,076	73,378	70,919	69,931	75,853	68,612
Non-interest expense	219,530	183,996	176,584	178,836	179,730	179,894	180,640	175,686	758,946	715,950	705,616
Income before income tax expense	75,162	87,570	67,899	49,343	116,439	119,276	125,100	125,877	279,974	486,692	441,633
Income tax expense	15,118	18,289	14,802	11,144	25,966	25,411	26,451	26,141	59,353	103,969	81,215
Net income	60,044	69,281	53,097	38,199	90,473	93,865	98,649	99,736	$ 220,621	$ 382,723	$ 360,418
Earnings applicable to common shareholders	$ 57,715	$ 66,890	$ 50,729	$ 36,021	$ 88,066	$ 91,442	$ 96,193	$ 97,549
Earnings per common share:
Earnings per common share, Basic (in dollars per share)	$ 0.64	$ 0.75	$ 0.57	$ 0.40	$ 0.96	$ 1.00	$ 1.05	$ 1.06	$ 2.35	$ 4.07	$ 3.83
Earnings per common share, Diluted (in dollars per share)	$ 0.64	$ 0.75	$ 0.57	$ 0.39	$ 0.96	$ 1.00	$ 1.05	$ 1.06	$ 2.35	$ 4.06	$ 3.81