INVESTMENT SECURITIES (Details 2) $ in Thousands	Dec. 31, 2016 USD ($) security	Dec. 31, 2015 USD ($) security
Fair Value
Less Than 12 Months	$ 2,162,896	$ 2,527,519
12 Months or More	253,038	228,733
Total	2,415,934	2,756,252
Gross Unrealized Losses
Less Than 12 Months	(51,760)	(16,075)
12 Months or More	(4,581)	(6,272)
Total	$ (56,341)	$ (22,347)
Number of securities in an unrealized loss position | security	170	186
Fair Value
Less Than 12 Months	$ 2,162,896
12 Months or More	253,038
Total	2,415,934
Gross Unrealized Losses
Less Than 12 Months	(51,760)
12 Months or More	(4,581)
Total	(56,341)
U.S. Treasury securities
Fair Value
Less Than 12 Months	670,268	$ 907,400
12 Months or More	0	20,282
Total	670,268	927,682
Gross Unrealized Losses
Less Than 12 Months	(9,829)	(4,250)
12 Months or More	0	(142)
Total	$ (9,829)	$ (4,392)
Number of securities in an unrealized loss position | security	26	39
U.S. government agency and U.S. government sponsored enterprise debt securities
Fair Value
Less Than 12 Months	$ 203,901	$ 541,385
12 Months or More	0	0
Total	203,901	541,385
Gross Unrealized Losses
Less Than 12 Months	(3,249)	(2,994)
12 Months or More	0	0
Total	$ (3,249)	$ (2,994)
U.S. government agency and U.S. government sponsored enterprise mortgage-backed securities
Gross Unrealized Losses
Number of securities in an unrealized loss position | security	82	85
U.S. government agency and U.S. government sponsored enterprise mortgage-backed securities - Commercial mortgage-backed securities
Fair Value
Less Than 12 Months	$ 202,106	$ 252,340
12 Months or More	29,201	20,793
Total	231,307	273,133
Gross Unrealized Losses
Less Than 12 Months	(5,452)	(2,562)
12 Months or More	(766)	(462)
Total	(6,218)	(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	629,324	535,842
12 Months or More	119,603	58,315
Total	748,927	594,157
Gross Unrealized Losses
Less Than 12 Months	(9,594)	(4,530)
12 Months or More	(1,955)	(1,871)
Total	(11,549)	(6,401)
Municipal securities
Fair Value
Less Than 12 Months	57,655	48,495
12 Months or More	2,692	14,739
Total	60,347	63,234
Gross Unrealized Losses
Less Than 12 Months	(1,699)	(437)
12 Months or More	(201)	(356)
Total	(1,900)	(793)
Non-agency residential mortgage-backed securities | Investment grade
Fair Value
Less Than 12 Months	5,033	5,123
12 Months or More	6,444	6,242
Total	11,477	11,365
Gross Unrealized Losses
Less Than 12 Months	(101)	(1)
12 Months or More	(14)	(172)
Total	(115)	$ (173)
Corporate debt securities
Gross Unrealized Losses
Number of securities in an unrealized loss position | security		12
Corporate debt securities | Investment grade
Fair Value
Less Than 12 Months	0	$ 149,358
12 Months or More	71,667	80,276
Total	71,667	229,634
Gross Unrealized Losses
Less Than 12 Months	0	(683)
12 Months or More	(375)	(864)
Total	(375)	(1,547)
Corporate debt securities | Non-investment grade
Fair Value
Less Than 12 Months	0	0
12 Months or More	9,173	9,642
Total	9,173	9,642
Gross Unrealized Losses
Less Than 12 Months	0	0
12 Months or More	(1,018)	(1,849)
Total	(1,018)	(1,849)
Foreign bonds | Investment grade
Fair Value
Less Than 12 Months	363,618	74,101
12 Months or More	14,258	9,713
Total	377,876	83,814
Gross Unrealized Losses
Less Than 12 Months	(21,327)	(506)
12 Months or More	(252)	(288)
Total	$ (21,579)	(794)
Number of securities in an unrealized loss position | security	13
Other securities
Fair Value
Less Than 12 Months	$ 30,991	13,475
12 Months or More	0	8,731
Total	30,991	22,206
Gross Unrealized Losses
Less Than 12 Months	(509)	(112)
12 Months or More	0	(268)
Total	(509)	$ (380)
Non-agency commercial mortgage-backed security
Fair Value
Less Than 12 Months	0
12 months or More	0
Total	0
Gross Unrealized Losses
Less than 12 months	0
12 Months or More	0
Total	$ 0