QUARTERLY FINANCIAL INFORMATION (unaudited) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012		Dec. 31, 2011
QUARTERLY FINANCIAL INFORMATION (unaudited)
Interest and dividend income	$ 293,203	$ 281,706	$ 255,353	$ 238,423	$ 276,521	$ 254,162	$ 266,362	$ 254,050	$ 1,068,685	$ 1,051,095		$ 1,080,448
Interest expense	28,195	27,456	27,709	29,132	31,577	32,254	33,205	35,132	112,492	132,168		177,422
Net interest income	265,008	254,250	227,644	209,291	244,944	221,908	233,157	218,918	956,193	918,927		903,026
Provision for (reversal of) loan losses, excluding covered loans	6,286	4,535	8,277	(762)	13,773	13,321	16,595	16,479	17,780	64,912
Provision for loan losses on covered loans	(820)	(964)	723	5,089	(689)	5,179	(1,095)	1,621	4,028	5,016		2,422
Net interest income after provision for loan losses	259,542	250,679	218,644	204,964	231,860	203,408	217,657	200,818	933,829	853,743		808,020
Noninterest (loss) income	(36,594)	(41,421)	(12,354)	(2,099)	(18,454)	2,751	(11,655)	21,740	(92,468)	(5,618)		10,924
Noninterest expense	124,384	100,352	94,420	96,355	105,206	100,956	101,608	114,763	415,511	422,533		435,610
Income before provision for income taxes	98,564	108,906	111,870	106,510	108,200	105,203	104,394	107,795	425,850	425,592		383,334
Provision for income taxes	22,782	35,749	37,855	34,419	36,300	34,093	33,837	39,712	130,805	143,942		138,100
Net income	75,782	73,157	74,015	72,091	71,900	71,110	70,557	68,083	295,045	281,650		245,234
Preferred stock dividends			1,714	1,714	1,715	1,714	1,714	1,714	3,428	6,857		6,857
Net income available to common stockholders	$ 75,782	$ 73,157	$ 72,301	$ 70,377	$ 70,185	$ 69,396	$ 68,843	$ 66,369	$ 291,617	$ 274,793		$ 238,377
Basic earnings per share	$ 0.55	$ 0.53	$ 0.52	$ 0.51	$ 0.50	$ 0.49	$ 0.48	$ 0.46	$ 2.11	$ 1.92	[1]	$ 1.62
Diluted earnings per share	$ 0.55	$ 0.53	$ 0.52	$ 0.50	$ 0.49	$ 0.48	$ 0.47	$ 0.45	$ 2.10	$ 1.89	[1]	$ 1.60

[1] On April 1, 2012, the Company revised its calculation of earnings per share to account for participating securities under the two-class method. This revision to the earnings per share calculation does not have an impact to previous periods as the amounts are immaterial.