AVAILABLE-FOR-SALE INVESTMENT SECURITIES (Details 4) (USD $) In Thousands, unless otherwise specified	Mar. 31, 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	$ 296,465	$ 414,390
Continuous unrealized loss position less than 12 months, Unrealized Losses	(1,319)	(2,051)
Continuous unrealized loss position 12 months or more, Fair Value	315,486	718,223
Continuous unrealized loss position 12 months or more, Unrealized Losses	(5,234)	(11,917)
Continuous unrealized loss position total, Fair Value	611,951	1,132,613
Continuous unrealized loss position total, Unrealized Losses	(6,553)	(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	61,684	170,260
Continuous unrealized loss position less than 12 months, Unrealized Losses	(37)	(266)
Continuous unrealized loss position 12 months or more, Fair Value	50,860	163,800
Continuous unrealized loss position 12 months or more, Unrealized Losses	(124)	(1,371)
Continuous unrealized loss position total, Fair Value	112,544	334,060
Continuous unrealized loss position total, Unrealized Losses	(161)	(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	144,114	69,438
Continuous unrealized loss position less than 12 months, Unrealized Losses	(383)	(504)
Continuous unrealized loss position 12 months or more, Fair Value	24,927	124,104
Continuous unrealized loss position 12 months or more, Unrealized Losses	(69)	(889)
Continuous unrealized loss position total, Fair Value	169,041	193,542
Continuous unrealized loss position total, Unrealized Losses	(452)	(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	14,119	45,405
Continuous unrealized loss position less than 12 months, Unrealized Losses	(141)	(257)
Continuous unrealized loss position 12 months or more, Fair Value	13,541	16,169
Continuous unrealized loss position 12 months or more, Unrealized Losses	(196)	(336)
Continuous unrealized loss position total, Fair Value	27,660	61,574
Continuous unrealized loss position total, Unrealized Losses	(337)	(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	40,969	81,927
Continuous unrealized loss position less than 12 months, Unrealized Losses	(97)	(270)
Continuous unrealized loss position 12 months or more, Fair Value	103,488	241,047
Continuous unrealized loss position 12 months or more, Unrealized Losses	(1,514)	(3,808)
Continuous unrealized loss position total, Fair Value	144,457	322,974
Continuous unrealized loss position total, Unrealized Losses	(1,611)	(4,078)
Percentage of the total available-for-sale investment securities portfolio	26.00%	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	26,905	6,391
Continuous unrealized loss position less than 12 months, Unrealized Losses	(335)	(26)
Continuous unrealized loss position 12 months or more, Fair Value	15,783	61,107
Continuous unrealized loss position 12 months or more, Unrealized Losses	(463)	(1,136)
Continuous unrealized loss position total, Fair Value	42,688	67,498
Continuous unrealized loss position total, Unrealized Losses	(798)	(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 12 months or more, Fair Value	6,985	7,217
Continuous unrealized loss position 12 months or more, Unrealized Losses	(106)	(135)
Continuous unrealized loss position total, Fair Value	6,985	7,217
Continuous unrealized loss position total, Unrealized Losses	(106)	(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		25,084
Continuous unrealized loss position less than 12 months, Unrealized Losses		(12)
Continuous unrealized loss position 12 months or more, Fair Value	90,401	90,098
Continuous unrealized loss position 12 months or more, Unrealized Losses	(739)	(1,042)
Continuous unrealized loss position total, Fair Value	90,401	115,182
Continuous unrealized loss position total, Unrealized Losses	(739)	(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	9,501	14,681
Continuous unrealized loss position 12 months or more, Unrealized Losses	(2,023)	(3,200)
Continuous unrealized loss position total, Fair Value	9,501	14,681
Continuous unrealized loss position total, Unrealized Losses	(2,023)	(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	8,674	15,885
Continuous unrealized loss position less than 12 months, Unrealized Losses	(326)	(716)
Continuous unrealized loss position total, Fair Value	8,674	15,885
Continuous unrealized loss position total, Unrealized Losses	$ (326)	$ (716)