QUARTERLY FINANCIAL INFORMATION (unaudited) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Quarterly Financial Information Disclosure [Abstract]
Interest and dividend income	$ 302,127	$ 280,317	$ 278,865	$ 276,172	$ 270,477	$ 264,632	$ 255,445	$ 263,261	$ 1,137,481	$ 1,053,815	$ 1,153,698
Interest expense	29,425	26,169	25,281	23,968	23,536	24,343	27,953	27,544	104,843	103,376	112,820
Net interest income before provision for credit losses	272,702	254,148	253,584	252,204	246,941	240,289	227,492	235,717	1,032,638	950,439	1,040,878
Provision for credit losses	10,461	9,525	6,053	1,440	(2,000)	7,736	3,494	4,987	27,479	14,217	49,158
Net interest income after provision for credit losses	262,241	244,623	247,531	250,764	248,941	232,553	223,998	230,730	1,005,159	936,222	991,720
Noninterest income	48,800	49,341	44,264	40,513	44,483	54,181	40,593	44,126	182,918	183,383	(11,714)
Noninterest expense	149,904	170,500	148,879	146,606	144,939	147,745	120,170	128,030	615,889	540,884	532,983
Income before income taxes	161,137	123,464	142,916	144,671	148,485	138,989	144,421	146,826	572,188	578,721	447,023
Income tax expense	50,403	13,321	39,632	37,155	56,680	44,892	45,673	46,799	140,511	194,044	101,145
NET INCOME	$ 110,734	$ 110,143	$ 103,284	$ 107,516	$ 91,805	$ 94,097	$ 98,748	$ 100,027	$ 431,677	$ 384,677	$ 345,878
EPS
Basic (in dollars per share)	$ 0.77	$ 0.76	$ 0.72	$ 0.75	$ 0.64	$ 0.65	$ 0.69	$ 0.70	$ 3.00	$ 2.67	$ 2.42
Diluted (in dollars per share)	$ 0.76	$ 0.76	$ 0.71	$ 0.74	$ 0.63	$ 0.65	$ 0.68	$ 0.69	$ 2.97	$ 2.66	$ 2.41
WEIGHTED AVERAGE NUMBER OF SHARES OUTSTANDING
Basic (in shares)	144,166	144,122	144,101	143,958	143,900	143,861	143,846	143,655	144,087	143,818	142,952
Diluted (in shares)	145,428	145,238	145,078	144,803	144,686	144,590	144,480	144,349	145,172	144,512	143,563
Dividends declared per common share (in dollars per share)	$ 0.20	$ 0.20	$ 0.20	$ 0.20	$ 0.20	$ 0.20	$ 0.20	$ 0.20	$ 0.80	$ 0.80	$ 0.72