INVESTMENT SECURITIES (Details 2) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Fair Value
Less Than 12 Months	$ 926,204	$ 2,527,519
12 Months or More	246,023	228,733
Total	1,172,227	2,756,252
Gross Unrealized Losses
Less Than 12 Months	(3,887)	(16,075)
12 Months or More	(5,634)	(6,272)
Total	(9,521)	(22,347)
U.S. Treasury securities
Fair Value
Less Than 12 Months	60,855	907,400
12 Months or More	30,570	20,282
Total	91,425	927,682
Gross Unrealized Losses
Less Than 12 Months	(42)	(4,250)
12 Months or More	(32)	(142)
Total	(74)	(4,392)
U.S. government agency and U.S. government sponsored enterprise debt securities
Fair Value
Less Than 12 Months	229,834	541,385
12 Months or More	9,189	0
Total	239,023	541,385
Gross Unrealized Losses
Less Than 12 Months	(571)	(2,994)
12 Months or More	(11)	0
Total	(582)	(2,994)
U.S. government agency and U.S. government sponsored enterprise mortgage-backed securities - Commercial mortgage-backed securities
Fair Value
Less Than 12 Months	103,881	252,340
12 Months or More	31,130	20,793
Total	135,011	273,133
Gross Unrealized Losses
Less Than 12 Months	(826)	(2,562)
12 Months or More	(390)	(462)
Total	(1,216)	(3,024)
U.S. government agency and U.S. government sponsored enterprise mortgage-backed securities - Residential mortgage-backed securities
Fair Value
Less Than 12 Months	255,839	535,842
12 Months or More	45,674	58,315
Total	301,513	594,157
Gross Unrealized Losses
Less Than 12 Months	(1,381)	(4,530)
12 Months or More	(930)	(1,871)
Total	(2,311)	(6,401)
Municipal securities
Fair Value
Less Than 12 Months	5,917	48,495
12 Months or More	15,794	14,739
Total	21,711	63,234
Gross Unrealized Losses
Less Than 12 Months	(31)	(437)
12 Months or More	(124)	(356)
Total	(155)	(793)
Non-agency residential mortgage-backed securities | Investment grade
Fair Value
Less Than 12 Months	13,945	5,123
12 Months or More	6,167	6,242
Total	20,112	11,365
Gross Unrealized Losses
Less Than 12 Months	(57)	(1)
12 Months or More	(19)	(172)
Total	(76)	(173)
Corporate debt securities | Investment grade
Fair Value
Less Than 12 Months	248,730	218,944
12 Months or More	90,899	89,989
Total	339,629	308,933
Gross Unrealized Losses
Less Than 12 Months	(976)	(1,189)
12 Months or More	(1,537)	(1,151)
Total	(2,513)	(2,340)
Corporate debt securities | Non-investment grade
Fair Value
Less Than 12 Months	0	0
12 Months or More	7,924	9,642
Total	7,924	9,642
Gross Unrealized Losses
Less Than 12 Months	0	0
12 Months or More	(2,267)	(1,849)
Total	(2,267)	(1,849)
Other securities
Fair Value
Less Than 12 Months	7,203	17,990
12 Months or More	8,676	8,731
Total	15,879	26,721
Gross Unrealized Losses
Less Than 12 Months	(3)	(112)
12 Months or More	(324)	(269)
Total	$ (327)	$ (381)