INVESTMENT SECURITIES (Details 2) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Fair Value
Less Than 12 Months	$ 596,906	$ 2,527,519
12 Months or More	162,182	228,733
Total	759,088	2,756,252
Gross Unrealized Losses
Less Than 12 Months	(2,377)	(16,075)
12 Months or More	(3,984)	(6,272)
Total	(6,361)	(22,347)
Fair Value
Less Than 12 Months	755,185
12 Months or More	162,182
Total	917,367
Gross Unrealized Losses
Less Than 12 Months	(3,306)
12 Months or More	(3,984)
Total	(7,290)
U.S. Treasury securities
Fair Value
Less Than 12 Months	0	907,400
12 Months or More	0	20,282
Total	0	927,682
Gross Unrealized Losses
Less Than 12 Months	0	(4,250)
12 Months or More	0	(142)
Total	0	(4,392)
US Government-sponsored Enterprises Debt Securities [Member]
Fair Value
Less Than 12 Months	85,210	541,385
12 Months or More	0	0
Total	85,210	541,385
Gross Unrealized Losses
Less Than 12 Months	(191)	(2,994)
12 Months or More	0	0
Total	(191)	(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	50,477	252,340
12 Months or More	24,377	20,793
Total	74,854	273,133
Gross Unrealized Losses
Less Than 12 Months	(476)	(2,562)
12 Months or More	(327)	(462)
Total	(803)	(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	295,399	535,842
12 Months or More	26,327	58,315
Total	321,726	594,157
Gross Unrealized Losses
Less Than 12 Months	(1,097)	(4,530)
12 Months or More	(626)	(1,871)
Total	(1,723)	(6,401)
Municipal securities
Fair Value
Less Than 12 Months	4,398	48,495
12 Months or More	2,896	14,739
Total	7,294	63,234
Gross Unrealized Losses
Less Than 12 Months	(50)	(437)
12 Months or More	(4)	(356)
Total	(54)	(793)
Non-agency residential mortgage-backed securities | Investment grade
Fair Value
Less Than 12 Months	7,470	5,123
12 Months or More	0	6,242
Total	7,470	11,365
Gross Unrealized Losses
Less Than 12 Months	(29)	(1)
12 Months or More	0	(172)
Total	(29)	(173)
Corporate debt securities | Investment grade
Fair Value
Less Than 12 Months	149,452	218,944
12 Months or More	91,236	89,989
Total	240,688	308,933
Gross Unrealized Losses
Less Than 12 Months	(533)	(1,189)
12 Months or More	(1,182)	(1,151)
Total	(1,715)	(2,340)
Corporate debt securities | Non-investment grade
Fair Value
Less Than 12 Months	0	0
12 Months or More	8,408	9,642
Total	8,408	9,642
Gross Unrealized Losses
Less Than 12 Months	0	0
12 Months or More	(1,783)	(1,849)
Total	(1,783)	(1,849)
Other securities
Fair Value
Less Than 12 Months	4,500	17,990
12 Months or More	8,938	8,731
Total	13,438	26,721
Gross Unrealized Losses
Less Than 12 Months	(1)	(112)
12 Months or More	(62)	(269)
Total	(63)	$ (381)
Non-agency commercial mortgage-backed security
Fair Value
Less Than 12 Months	158,279
12 Months or More	0
Total	158,279
Gross Unrealized Losses
Less Than 12 Months	(929)
12 Months or More	0
Total	$ (929)