INVESTMENT SECURITIES (Details 4) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Continuous unrealized loss position, fair values of investment securities available-for-sale
Continuous unrealized loss position less than 12 months, fair value	$ 414,390	$ 1,803,073
Continuous unrealized loss position less than 12 months, unrealized losses	(2,051)	(45,167)
Continuous unrealized loss position 12 months or more, fair value	718,223	250,361
Continuous unrealized loss position 12 months or more, unrealized losses	(11,917)	(19,729)
Continuous unrealized loss position total, fair value	1,132,613	2,053,434
Continuous unrealized loss position total, unrealized losses	(13,968)	(64,896)
U.S. Treasury securities
Continuous unrealized loss position, fair values of investment securities available-for-sale
Continuous unrealized loss position less than 12 months, fair value	170,260	337,248
Continuous unrealized loss position less than 12 months, unrealized losses	(266)	(3,622)
Continuous unrealized loss position 12 months or more, fair value	163,800
Continuous unrealized loss position 12 months or more, unrealized losses	(1,371)
Continuous unrealized loss position total, fair value	334,060	337,248
Continuous unrealized loss position total, unrealized losses	(1,637)	(3,622)
Total investment securities available-for-sale portfolio (as a percent)	33.00%	18.00%
U.S. government agency and U.S. government sponsored enterprise debt securities
Continuous unrealized loss position, fair values of investment securities available-for-sale
Continuous unrealized loss position less than 12 months, fair value	69,438	387,097
Continuous unrealized loss position less than 12 months, unrealized losses	(504)	(12,726)
Continuous unrealized loss position 12 months or more, fair value	124,104
Continuous unrealized loss position 12 months or more, unrealized losses	(889)
Continuous unrealized loss position total, fair value	193,542	387,097
Continuous unrealized loss position total, unrealized losses	(1,393)	(12,726)
U.S. government agency and U.S. government sponsored enterprise mortgage-backed securities - Commercial mortgage-backed securities
Continuous unrealized loss position, fair values of investment securities available-for-sale
Continuous unrealized loss position less than 12 months, fair value	45,405	114,754
Continuous unrealized loss position less than 12 months, unrealized losses	(257)	(3,280)
Continuous unrealized loss position 12 months or more, fair value	16,169	16,065
Continuous unrealized loss position 12 months or more, unrealized losses	(336)	(1,169)
Continuous unrealized loss position total, fair value	61,574	130,819
Continuous unrealized loss position total, unrealized losses	(593)	(4,449)
U.S. government agency and U.S. government sponsored enterprise mortgage-backed securities - Residential mortgage-backed securities
Continuous unrealized loss position, fair values of investment securities available-for-sale
Continuous unrealized loss position less than 12 months, fair value	81,927	502,285
Continuous unrealized loss position less than 12 months, unrealized losses	(270)	(10,570)
Continuous unrealized loss position 12 months or more, fair value	241,047	92,540
Continuous unrealized loss position 12 months or more, unrealized losses	(3,808)	(4,357)
Continuous unrealized loss position total, fair value	322,974	594,825
Continuous unrealized loss position total, unrealized losses	(4,078)	(14,927)
Total investment securities available-for-sale portfolio (as a percent)	30.00%	32.00%
Municipal securities
Continuous unrealized loss position, fair values of investment securities available-for-sale
Continuous unrealized loss position less than 12 months, fair value	6,391	173,782
Continuous unrealized loss position less than 12 months, unrealized losses	(26)	(10,765)
Continuous unrealized loss position 12 months or more, fair value	61,107	47,892
Continuous unrealized loss position 12 months or more, unrealized losses	(1,136)	(6,768)
Continuous unrealized loss position total, fair value	67,498	221,674
Continuous unrealized loss position total, unrealized losses	(1,162)	(17,533)
Other residential mortgage-backed securities | Investment grade
Continuous unrealized loss position, fair values of investment securities available-for-sale
Continuous unrealized loss position less than 12 months, fair value		46,327
Continuous unrealized loss position less than 12 months, unrealized losses		(1,802)
Continuous unrealized loss position 12 months or more, fair value	7,217
Continuous unrealized loss position 12 months or more, unrealized losses	(135)
Continuous unrealized loss position total, fair value	7,217	46,327
Continuous unrealized loss position total, unrealized losses	(135)	(1,802)
Corporate debt securities | Investment grade
Continuous unrealized loss position, fair values of investment securities available-for-sale
Continuous unrealized loss position less than 12 months, fair value	25,084	193,482
Continuous unrealized loss position less than 12 months, unrealized losses	(12)	(1,538)
Continuous unrealized loss position 12 months or more, fair value	90,098	79,442
Continuous unrealized loss position 12 months or more, unrealized losses	(1,042)	(1,806)
Continuous unrealized loss position total, fair value	115,182	272,924
Continuous unrealized loss position total, unrealized losses	(1,054)	(3,344)
Corporate debt securities | Non-investment grade
Continuous unrealized loss position, fair values of investment securities available-for-sale
Continuous unrealized loss position 12 months or more, fair value	14,681	14,422
Continuous unrealized loss position 12 months or more, unrealized losses	(3,200)	(5,629)
Continuous unrealized loss position total, fair value	14,681	14,422
Continuous unrealized loss position total, unrealized losses	(3,200)	(5,629)
Total investment securities available-for-sale portfolio (as a percent)	1.00%	1.00%
Other securities
Continuous unrealized loss position, fair values of investment securities available-for-sale
Continuous unrealized loss position less than 12 months, fair value	15,885	48,098
Continuous unrealized loss position less than 12 months, unrealized losses	(716)	(864)
Continuous unrealized loss position total, fair value	15,885	48,098
Continuous unrealized loss position total, unrealized losses	$ (716)	$ (864)