Quarterly Financial Information (Unaudited) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ 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 and dividend income	$ 467,233	$ 476,912	$ 474,844	$ 463,311	$ 457,334	$ 422,185	$ 400,311	$ 371,873	$ 1,882,300	$ 1,651,703	$ 1,325,119
Interest expense	99,014	107,105	107,518	100,850	87,918	73,465	58,632	45,180	414,487	265,195	140,050
Net interest income before provision for credit losses	368,219	369,807	367,326	362,461	369,416	348,720	341,679	326,693	1,467,813	1,386,508	1,185,069
Provision for credit losses	18,577	38,284	19,245	22,579	17,959	10,542	15,536	20,218	98,685	64,255	46,266
Net interest income after provision for credit losses	349,642	331,523	348,081	339,882	351,457	338,178	326,143	306,475	1,369,128	1,322,253	1,138,803
Noninterest income	63,013	51,474	52,759	42,131	41,695	46,502	48,268	74,444	209,377	210,909	257,748
Noninterest expense	193,373	176,630	177,663	186,922	188,097	179,815	177,419	169,135	734,588	714,466	661,451
Income before income taxes	219,282	206,367	223,177	195,091	205,055	204,865	196,992	211,784	843,917	818,696	735,100
Income tax expense	31,067	34,951	72,797	31,067	32,037	33,563	24,643	24,752	169,882	114,995	229,476
NET INCOME	$ 188,215	$ 171,416	$ 150,380	$ 164,024	$ 173,018	$ 171,302	$ 172,349	$ 187,032	$ 674,035	$ 703,701	$ 505,624
EPS
Basic (in dollars per share)	$ 1.29	$ 1.18	$ 1.03	$ 1.13	$ 1.19	$ 1.18	$ 1.19	$ 1.29	$ 4.63	$ 4.86	$ 3.50
Diluted (in dollars per share)	$ 1.29	$ 1.17	$ 1.03	$ 1.12	$ 1.18	$ 1.17	$ 1.18	$ 1.28	$ 4.61	$ 4.81	$ 3.47
WEIGHTED-AVERAGE NUMBER OF SHARES OUTSTANDING
Basic (in shares)	145,624	145,559	145,546	145,256	144,960	144,921	144,899	144,664	145,497	144,862	144,444
Diluted (in shares)	146,318	146,120	146,052	145,921	146,133	146,173	146,091	145,939	146,179	146,169	145,913