INVESTMENT SECURITIES (Details 4) (USD $) In Thousands, unless otherwise specified	Mar. 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	$ 1,412,651	$ 1,803,074
Continuous unrealized loss position less than 12 months, unrealized losses	(27,692)	(45,167)
Continuous unrealized loss position 12 months or more, fair value	294,599	250,361
Continuous unrealized loss position 12 months or more, unrealized losses	(17,551)	(19,729)
Continuous unrealized loss position total, fair value	1,707,250	2,053,435
Continuous unrealized loss position total, unrealized losses	(45,243)	(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	346,069	337,248
Continuous unrealized loss position less than 12 months, unrealized losses	(3,145)	(3,622)
Continuous unrealized loss position total, fair value	346,069	337,248
Continuous unrealized loss position total, unrealized losses	(3,145)	(3,622)
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	252,148	387,097
Continuous unrealized loss position less than 12 months, unrealized losses	(7,548)	(12,726)
Continuous unrealized loss position total, fair value	252,148	387,097
Continuous unrealized loss position total, unrealized losses	(7,548)	(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	81,367	114,754
Continuous unrealized loss position less than 12 months, unrealized losses	(1,752)	(3,280)
Continuous unrealized loss position 12 months or more, fair value	16,082	16,065
Continuous unrealized loss position 12 months or more, unrealized losses	(909)	(1,169)
Continuous unrealized loss position total, fair value	97,449	130,819
Continuous unrealized loss position total, unrealized losses	(2,661)	(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	417,992	502,285
Continuous unrealized loss position less than 12 months, unrealized losses	(7,447)	(10,570)
Continuous unrealized loss position 12 months or more, fair value	119,255	92,540
Continuous unrealized loss position 12 months or more, unrealized losses	(4,784)	(4,357)
Continuous unrealized loss position total, fair value	537,247	594,825
Continuous unrealized loss position total, unrealized losses	(12,231)	(14,927)
Municipal securities
Continuous unrealized loss position, fair values of investment securities available-for-sale
Continuous unrealized loss position less than 12 months, fair value	110,001	173,782
Continuous unrealized loss position less than 12 months, unrealized losses	(4,462)	(10,765)
Continuous unrealized loss position 12 months or more, fair value	64,839	47,892
Continuous unrealized loss position 12 months or more, unrealized losses	(5,079)	(6,768)
Continuous unrealized loss position total, fair value	174,840	221,674
Continuous unrealized loss position total, unrealized losses	(9,541)	(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	57,007	46,328
Continuous unrealized loss position less than 12 months, unrealized losses	(1,443)	(1,802)
Continuous unrealized loss position total, fair value	57,007	46,328
Continuous unrealized loss position total, unrealized losses	(1,443)	(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	128,623	193,482
Continuous unrealized loss position less than 12 months, unrealized losses	(1,276)	(1,538)
Continuous unrealized loss position 12 months or more, fair value	79,554	79,442
Continuous unrealized loss position 12 months or more, unrealized losses	(1,686)	(1,806)
Continuous unrealized loss position total, fair value	208,177	272,924
Continuous unrealized loss position total, unrealized losses	(2,962)	(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	14,869	14,422
Continuous unrealized loss position 12 months or more, unrealized losses	(5,093)	(5,629)
Continuous unrealized loss position total, fair value	14,869	14,422
Continuous unrealized loss position total, unrealized losses	(5,093)	(5,629)
Other securities
Continuous unrealized loss position, fair values of investment securities available-for-sale
Continuous unrealized loss position less than 12 months, fair value	19,444	48,098
Continuous unrealized loss position less than 12 months, unrealized losses	(619)	(864)
Continuous unrealized loss position total, fair value	19,444	48,098
Continuous unrealized loss position total, unrealized losses	$ (619)	$ (864)