Selected Quarterly Consolidated Financial Information (Unaudited) (Details) - USD ($) $ 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
Selected Quarterly Financial Information [Abstract]
Interest income	$ 282,000	$ 294,136	$ 292,257	$ 286,190	$ 280,392	$ 268,363	$ 260,491	$ 245,921	$ 1,154,583	$ 1,055,167	$ 913,605
Interest expense	50,750	53,597	50,470	44,639	43,261	37,991	35,481	31,753	199,456	148,486	117,318
Net interest income	231,250	240,539	241,787	241,551	237,131	230,372	225,010	214,168	955,127	906,681	796,287
Provision for loan and lease losses	6,000	11,300	11,900	8,600	10,000	10,500	10,500	11,000	37,800	42,000	40,900
Non-interest income	70,919	69,931	75,853	68,612	73,163	72,284	68,374	68,747
Non-interest expense	179,730	179,894	180,640	175,686	174,759	178,783	180,459	171,615	715,950	705,616	661,075
Income before income tax expense	116,439	119,276	125,100	125,877	125,535	113,373	102,425	100,300	486,692	441,633	353,790
Income tax expense	25,966	25,411	26,451	26,141	26,697	13,700	20,743	20,075	103,969	81,215	98,351
Net income	90,473	93,865	98,649	99,736	98,838	99,673	81,682	80,225	382,723	360,418	255,439
Earnings applicable to common shareholders	$ 88,066	$ 91,442	$ 96,193	$ 97,549	$ 96,666	$ 97,460	$ 79,489	$ 78,083	$ 372,985	$ 351,703	$ 246,831
Earnings per common share:
Earnings per common share, Basic (in dollars per share)	$ 0.96	$ 1.00	$ 1.05	$ 1.06	$ 1.05	$ 1.06	$ 0.87	$ 0.85	$ 4.07	$ 3.83	$ 2.68
Earnings per common share, Diluted (in dollars per share)	$ 0.96	$ 1.00	$ 1.05	$ 1.06	$ 1.05	$ 1.06	$ 0.86	$ 0.85	$ 4.06	$ 3.81	$ 2.67