QUARTERLY FINANCIAL INFORMATION (unaudited) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
QUARTERLY FINANCIAL INFORMATION (unaudited)
Interest and dividend income	$ 276,521	$ 254,162	$ 266,362	$ 254,050	$ 268,904	$ 282,741	$ 274,468	$ 254,335	$ 1,051,095	$ 1,080,448	$ 1,095,831
Interest expense	31,577	32,254	33,205	35,132	39,830	44,959	47,132	45,501	132,168	177,422	201,117
Net interest income	244,944	221,908	233,157	218,918	229,074	237,782	227,336	208,834	918,927	903,026	894,714
Provision for loan losses, excluding covered loans	13,773	13,321	16,595	16,479	19,787	22,297	25,528	24,972
(Reversal of) provision for loan losses on covered loans	(689)	5,179	(1,095)	1,621	213	(297)	972	1,534
Net interest income after provision for loan losses	231,860	203,408	217,657	200,818	209,074	215,782	200,836	182,328	853,743	808,020	694,555
Noninterest (loss) income	(18,254)	2,751	(11,655)	21,740	937	(13,545)	12,491	11,041	(5,618)	10,924	39,270
Noninterest expense	105,206	100,956	101,608	114,763	106,672	104,552	117,597	106,789	422,533	435,610	477,916
Income before provision for income taxes	108,200	105,203	104,394	107,795	103,339	97,685	95,730	86,580	425,592	383,334	255,909
Provision for income taxes	36,300	34,093	33,837	39,712	37,133	35,253	35,205	30,509	143,942	138,100	91,345
Net income	71,900	71,110	70,557	68,083	66,206	62,432	60,525	56,071	281,650	245,234	164,564
Preferred stock dividends	1,715	1,714	1,714	1,714	1,714	1,714	1,714	1,715	6,857	6,857	43,126
Net income available to common stockholders	$ 70,185	$ 69,396	$ 68,843	$ 66,369	$ 64,492	$ 60,718	$ 58,811	$ 54,356	$ 274,793	$ 238,377	$ 121,438
Basic earnings per share	$ 0.50	$ 0.49	$ 0.48	$ 0.46	$ 0.44	$ 0.41	$ 0.40	$ 0.37	$ 1.92	$ 1.62	$ 0.88
Diluted earnings per share	$ 0.49	$ 0.48	$ 0.47	$ 0.45	$ 0.43	$ 0.41	$ 0.39	$ 0.37	$ 1.89	$ 1.60	$ 0.83