QUARTERLY FINANCIAL INFORMATION (unaudited) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
QUARTERLY FINANCIAL INFORMATION (unaudited)
Interest and dividend income	$ 268,904	$ 282,741	$ 274,468	$ 254,335	$ 292,195	$ 231,400	$ 253,533	$ 318,703	$ 1,080,448	$ 1,095,831	$ 722,818
Interest expense	39,830	44,959	47,132	45,501	45,633	48,595	49,910	56,979	177,422	201,117	237,129
Net interest income	229,074	237,782	227,336	208,834	246,562	182,805	203,623	261,724	903,026	894,714	485,689
Provision for loan losses	20,000	22,000	26,500	26,506	29,834	38,648	55,256	76,421	95,006	200,159	528,666
Net interest income after provision for loan losses	209,074	215,782	200,836	182,328	216,728	144,157	148,367	185,303	808,020	694,555	(42,977)
Noninterest (loss) income	937	(13,545)	12,491	11,041	(17,279)	29,315	35,685	(8,451)	10,924	39,270	390,953
Noninterest expense	106,672	104,552	117,597	106,789	113,743	99,945	125,318	138,910	435,610	477,916	243,254
Income before provision for income taxes	103,339	97,685	95,730	86,580	85,706	73,527	58,734	37,942	383,334	255,909	104,722
Provision for income taxes	37,133	35,253	35,205	30,509	29,357	26,576	22,386	13,026	138,100	91,345	22,714
Net income	66,206	62,432	60,525	56,071	56,349	46,951	36,348	24,916	245,234	164,564	76,642
Preferred stock dividends and amortization of preferred stock discount	1,714	1,714	1,714	1,715	24,109	6,732	6,147	6,138	6,857	43,126	49,115
Net income available to common stockholders	$ 64,492	$ 60,718	$ 58,811	$ 54,356	$ 32,240	$ 40,219	$ 30,201	$ 18,778	$ 238,377	$ 121,438	$ 27,527
Basic earnings per share	$ 0.44	$ 0.41	$ 0.40	$ 0.37	$ 0.22	$ 0.27	$ 0.21	$ 0.17	$ 1.62	$ 0.88	$ 0.35
Diluted earnings per share	$ 0.43	$ 0.41	$ 0.39	$ 0.37	$ 0.22	$ 0.27	$ 0.21	$ 0.13	$ 1.60	$ 0.83	$ 0.33