Quarterly Financial Information (Unaudited) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Quarterly Financial Information Disclosure [Abstract]
Interest and dividend income	$ 359,765	$ 339,910	$ 322,775	$ 302,669	$ 302,127	$ 280,317	$ 278,865	$ 276,172	$ 1,325,119	$ 1,137,481	$ 1,053,815
Interest expense	40,064	36,755	32,684	30,547	29,425	26,169	25,281	23,968	140,050	104,843	103,376
Net interest income before provision for credit losses	319,701	303,155	290,091	272,122	272,702	254,148	253,584	252,204	1,185,069	1,032,638	950,439
Provision for credit losses	15,517	12,996	10,685	7,068	10,461	9,525	6,053	1,440	46,266	27,479	14,217
Net interest income after provision for credit losses	304,184	290,159	279,406	265,054	262,241	244,623	247,531	250,764	1,138,803	1,005,159	936,222
Noninterest income	45,359	49,624	47,400	116,023	48,800	49,341	44,264	40,513	258,406	182,918	183,383
Noninterest expense	175,416	164,499	169,121	153,073	149,904	170,500	148,879	146,606	662,109	615,889	540,884
Income before income taxes	174,127	175,284	157,685	228,004	161,137	123,464	142,916	144,671	735,100	572,188	578,721
Income tax expense	89,229	42,624	39,355	58,268	50,403	13,321	39,632	37,155	229,476	140,511	194,044
NET INCOME	$ 84,898	$ 132,660	$ 118,330	$ 169,736	$ 110,734	$ 110,143	$ 103,284	$ 107,516	$ 505,624	$ 431,677	$ 384,677
EPS
Basic (in dollars per share)	$ 0.59	$ 0.92	$ 0.82	$ 1.18	$ 0.77	$ 0.76	$ 0.72	$ 0.75	$ 3.50	$ 3.00	$ 2.67
Diluted (in dollars per share)	$ 0.58	$ 0.91	$ 0.81	$ 1.16	$ 0.76	$ 0.76	$ 0.71	$ 0.74	$ 3.47	$ 2.97	$ 2.66
WEIGHTED-AVERAGE NUMBER OF SHARES OUTSTANDING
Basic (in shares)	144,542	144,498	144,485	144,249	144,166	144,122	144,101	143,958	144,444	144,087	143,818
Diluted (in shares)	146,030	145,882	145,740	145,732	145,428	145,238	145,078	144,803	145,913	145,172	144,512
Dividends declared per common share (in dollars per share)	$ 0.2	$ 0.20	$ 0.20	$ 0.20	$ 0.20	$ 0.20	$ 0.20	$ 0.20	$ 0.8	$ 0.8	$ 0.8