Quarterly Financial Information (Unaudited) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ 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 and dividend income	$ 457,334	$ 422,185	$ 400,311	$ 371,873	$ 359,765	$ 339,910	$ 322,775	$ 302,669	$ 1,651,703	$ 1,325,119	$ 1,137,481
Interest expense	87,918	73,465	58,632	45,180	40,064	36,755	32,684	30,547	265,195	140,050	104,843
Net interest income before provision for credit losses	369,416	348,720	341,679	326,693	319,701	303,155	290,091	272,122	1,386,508	1,185,069	1,032,638
Provision for credit losses	17,959	10,542	15,536	20,218	15,517	12,996	10,685	7,068	64,255	46,266	27,479
Net interest income after provision for credit losses	351,457	338,178	326,143	306,475	304,184	290,159	279,406	265,054	1,322,253	1,138,803	1,005,159
Noninterest income	41,695	46,502	48,268	74,444	45,206	49,470	47,244	115,828	210,909	257,748	182,278
Noninterest expense	188,097	179,815	177,419	169,135	175,263	164,345	168,965	152,878	714,466	661,451	615,249
Income before income taxes	205,055	204,865	196,992	211,784	174,127	175,284	157,685	228,004	818,696	735,100	572,188
Income tax expense	32,037	33,563	24,643	24,752	89,229	42,624	39,355	58,268	114,995	229,476	140,511
NET INCOME	$ 173,018	$ 171,302	$ 172,349	$ 187,032	$ 84,898	$ 132,660	$ 118,330	$ 169,736	$ 703,701	$ 505,624	$ 431,677
EPS
Basic (in dollars per share)	$ 1.19	$ 1.18	$ 1.19	$ 1.29	$ 0.59	$ 0.92	$ 0.82	$ 1.18	$ 4.86	$ 3.50	$ 3.00
Diluted (in dollars per share)	$ 1.18	$ 1.17	$ 1.18	$ 1.28	$ 0.58	$ 0.91	$ 0.81	$ 1.16	$ 4.81	$ 3.47	$ 2.97
WEIGHTED-AVERAGE NUMBER OF SHARES OUTSTANDING
Basic (in shares)	144,960	144,921	144,899	144,664	144,542	144,498	144,485	144,249	144,862	144,444	144,087
Diluted (in shares)	146,133	146,173	146,091	145,939	146,030	145,882	145,740	145,732	146,169	145,913	145,172
Dividends declared per common share (in dollars per share)	$ 0.23	$ 0.23	$ 0.20	$ 0.20	$ 0.20	$ 0.20	$ 0.20	$ 0.20	$ 0.86	$ 0.80	$ 0.80