QUARTERLY FINANCIAL INFORMATION (unaudited) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015		Dec. 31, 2014		Dec. 31, 2013
Quarterly Financial Information Disclosure [Abstract]
Interest and dividend income	$ 270,477	$ 264,632	$ 255,445	$ 263,261	$ 287,135	$ 285,948	$ 294,442	$ 286,173	$ 1,053,815		$ 1,153,698		$ 1,068,685
Interest expense	23,536	24,343	27,953	27,544	27,647	28,974	27,992	28,207	103,376		112,820		112,492
Net interest income before provision for credit losses	246,941	240,289	227,492	235,717	259,488	256,974	266,450	257,966	950,439		1,040,878		956,193
(Reversal of) provision for credit losses	(2,000)	7,736	3,494	4,987	19,000	15,225	8,000	6,933	14,217		49,158		22,364
Net interest income after provision for credit losses	248,941	232,553	223,998	230,730	240,488	241,749	258,450	251,033	936,222		991,720		933,829
Noninterest income (loss)	44,483	54,181	40,593	44,126	7,805	10,342	(14,945)	(14,916)	183,383		(11,714)		(92,468)
Noninterest expense	144,939	147,745	120,170	128,030	125,698	166,792	120,539	119,954	540,884	[1]	532,983	[1]	394,215	[1]
Income before income taxes	148,485	138,989	144,421	146,826	122,595	85,299	122,966	116,163	578,721	[1]	447,023	[1]	447,146	[1]
INCOME TAX EXPENSE	56,680	44,892	45,673	46,799	27,093	(6,601)	38,661	41,992	194,044	[1]	101,145	[1]	153,822	[1]
NET INCOME	$ 91,805	$ 94,097	$ 98,748	$ 100,027	$ 95,502	$ 91,900	$ 84,305	$ 74,171	$ 384,677	[1]	$ 345,878	[1]	$ 293,324	[1]
Earnings per share
BASIC (in dollars per share)	$ 0.64	$ 0.65	$ 0.69	$ 0.70	$ 0.67	$ 0.64	$ 0.59	$ 0.52	$ 2.67	[1]	$ 2.42	[1]	$ 2.10	[1]
DILUTED (in dollars per share)	$ 0.63	$ 0.65	$ 0.68	$ 0.69	$ 0.66	$ 0.64	$ 0.59	$ 0.52	$ 2.66	[1]	$ 2.41	[1]	$ 2.09	[1]
Basic weighted-average common shares outstanding (in shares)	143,900	143,861	143,846	143,655	143,432	143,210	143,187	141,962	143,818		142,952		137,342
Diluted average common shares outstanding (in shares)	144,686	144,590	144,480	144,349	144,116	143,810	143,689	142,632	144,512		143,563		139,574
DIVIDENDS DECLARED PER COMMON SHARE (in dollars per share)	$ 0.20	$ 0.20	$ 0.20	$ 0.20	$ 0.18	$ 0.18	$ 0.18	$ 0.18	$ 0.80		$ 0.72		$ 0.60

[1] Prior period was restated to reflect the retrospective application of adopting the new accounting guidance related to the Company’s investments in qualified affordable housing projects Accounting Standards Update (“ASU”) 2014-01. Please see Note 9 — Investments in Qualified Affordable Housing Partnerships, Tax Credit and Other Investments, Net to the Consolidated Financial Statements for additional information.