AVAILABLE-FOR-SALE INVESTMENT SECURITIES (Details 4) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Gross unrealized losses and related fair values of individual securities in a continuous unrealized loss position
Continuous unrealized loss position less than 12 months, Fair Value	$ 626,362	$ 414,390
Continuous unrealized loss position less than 12 months, Gross Unrealized Losses	(4,766)	(2,051)
Continuous unrealized loss position 12 months or more, Fair Value	325,703	718,223
Continuous unrealized loss position 12 months or more, Gross Unrealized Losses	(6,184)	(11,917)
Continuous unrealized loss position total, Fair Value	952,065	1,132,613
Continuous unrealized loss position total, Gross Unrealized Losses	(10,950)	(13,968)
U.S. Treasury securities
Gross unrealized losses and related fair values of individual securities in a continuous unrealized loss position
Continuous unrealized loss position less than 12 months, Fair Value	61,141	170,260
Continuous unrealized loss position less than 12 months, Gross Unrealized Losses	(30)	(266)
Continuous unrealized loss position 12 months or more, Fair Value	50,766	163,800
Continuous unrealized loss position 12 months or more, Gross Unrealized Losses	(142)	(1,371)
Continuous unrealized loss position total, Fair Value	111,907	334,060
Continuous unrealized loss position total, Gross Unrealized Losses	(172)	(1,637)
U.S. government agency and U.S. government sponsored enterprise debt securities
Gross unrealized losses and related fair values of individual securities in a continuous unrealized loss position
Continuous unrealized loss position less than 12 months, Fair Value	256,518	69,438
Continuous unrealized loss position less than 12 months, Gross Unrealized Losses	(1,106)	(504)
Continuous unrealized loss position 12 months or more, Fair Value	24,887	124,104
Continuous unrealized loss position 12 months or more, Gross Unrealized Losses	(110)	(889)
Continuous unrealized loss position total, Fair Value	281,405	193,542
Continuous unrealized loss position total, Gross Unrealized Losses	(1,216)	(1,393)
U.S. government agency and U.S. government sponsored enterprise mortgage-backed securities - Commercial mortgage-backed securities
Gross unrealized losses and related fair values of individual securities in a continuous unrealized loss position
Continuous unrealized loss position less than 12 months, Fair Value	86,572	45,405
Continuous unrealized loss position less than 12 months, Gross Unrealized Losses	(504)	(257)
Continuous unrealized loss position 12 months or more, Fair Value	21,982	16,169
Continuous unrealized loss position 12 months or more, Gross Unrealized Losses	(441)	(336)
Continuous unrealized loss position total, Fair Value	108,554	61,574
Continuous unrealized loss position total, Gross Unrealized Losses	(945)	(593)
U.S. government agency and U.S. government sponsored enterprise mortgage-backed securities - Residential mortgage-backed securities
Gross unrealized losses and related fair values of individual securities in a continuous unrealized loss position
Continuous unrealized loss position less than 12 months, Fair Value	135,426	81,927
Continuous unrealized loss position less than 12 months, Gross Unrealized Losses	(1,115)	(270)
Continuous unrealized loss position 12 months or more, Fair Value	96,853	241,047
Continuous unrealized loss position 12 months or more, Gross Unrealized Losses	(1,956)	(3,808)
Continuous unrealized loss position total, Fair Value	232,279	322,974
Continuous unrealized loss position total, Gross Unrealized Losses	$ (3,071)	$ (4,078)
Percentage of the total available-for-sale investment securities portfolio	23.00%	30.00%
Municipal securities
Gross unrealized losses and related fair values of individual securities in a continuous unrealized loss position
Continuous unrealized loss position less than 12 months, Fair Value	$ 52,924	$ 6,391
Continuous unrealized loss position less than 12 months, Gross Unrealized Losses	(1,906)	(26)
Continuous unrealized loss position 12 months or more, Fair Value	15,262	61,107
Continuous unrealized loss position 12 months or more, Gross Unrealized Losses	(955)	(1,136)
Continuous unrealized loss position total, Fair Value	68,186	67,498
Continuous unrealized loss position total, Gross Unrealized Losses	$ (2,861)	$ (1,162)
Percentage of the total available-for-sale investment securities portfolio	7.00%	10.00%
Other residential mortgage-backed securities | Investment grade
Gross unrealized losses and related fair values of individual securities in a continuous unrealized loss position
Continuous unrealized loss position less than 12 months, Fair Value	$ 5,684
Continuous unrealized loss position less than 12 months, Gross Unrealized Losses	(16)
Continuous unrealized loss position 12 months or more, Fair Value	6,589	$ 7,217
Continuous unrealized loss position 12 months or more, Gross Unrealized Losses	(279)	(135)
Continuous unrealized loss position total, Fair Value	12,273	7,217
Continuous unrealized loss position total, Gross Unrealized Losses	(295)	(135)
Corporate debt securities | Investment grade
Gross unrealized losses and related fair values of individual securities in a continuous unrealized loss position
Continuous unrealized loss position less than 12 months, Fair Value	10,050	25,084
Continuous unrealized loss position less than 12 months, Gross Unrealized Losses	(36)	(12)
Continuous unrealized loss position 12 months or more, Fair Value	90,618	90,098
Continuous unrealized loss position 12 months or more, Gross Unrealized Losses	(522)	(1,042)
Continuous unrealized loss position total, Fair Value	100,668	115,182
Continuous unrealized loss position total, Gross Unrealized Losses	(558)	(1,054)
Corporate debt securities | Non-investment grade
Gross unrealized losses and related fair values of individual securities in a continuous unrealized loss position
Continuous unrealized loss position 12 months or more, Fair Value	10,025	14,681
Continuous unrealized loss position 12 months or more, Gross Unrealized Losses	(1,500)	(3,200)
Continuous unrealized loss position total, Fair Value	10,025	14,681
Continuous unrealized loss position total, Gross Unrealized Losses	$ (1,500)	$ (3,200)
Percentage of the total available-for-sale investment securities portfolio	1.00%	1.00%
Other securities
Gross unrealized losses and related fair values of individual securities in a continuous unrealized loss position
Continuous unrealized loss position less than 12 months, Fair Value	$ 18,047	$ 15,885
Continuous unrealized loss position less than 12 months, Gross Unrealized Losses	(53)	(716)
Continuous unrealized loss position 12 months or more, Fair Value	8,721
Continuous unrealized loss position 12 months or more, Gross Unrealized Losses	(279)
Continuous unrealized loss position total, Fair Value	26,768	15,885
Continuous unrealized loss position total, Gross Unrealized Losses	$ (332)	$ (716)