INVESTMENT SECURITIES (Details) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities
Amortized Cost	$ 3,193,553	$ 3,783,829
Gross Unrealized Gains	21,206	11,744
Gross Unrealized Losses	(9,521)	(22,347)
Available-for-sale investment securities, at fair value	3,205,238	3,773,226
Schedule of Held-to-maturity Securities
Amortized Cost	160,135	0
Fair Value	160,135	0
Investment Securities
Amortized Cost	3,353,688
Gross Unrealized Gains	21,206
Gross Unrealized Losses	(9,521)
Fair Value	3,365,373
U.S. Treasury securities
Schedule of Available-for-sale Securities
Amortized Cost	514,827	1,002,874
Gross Unrealized Gains	2,002	33
Gross Unrealized Losses	(74)	(4,392)
Available-for-sale investment securities, at fair value	516,755	998,515
U.S. government agency and U.S. government sponsored enterprise debt securities
Schedule of Available-for-sale Securities
Amortized Cost	787,846	771,288
Gross Unrealized Gains	1,671	555
Gross Unrealized Losses	(582)	(2,994)
Available-for-sale investment securities, at fair value	788,935	768,849
U.S. government agency and U.S. government sponsored enterprise mortgage-backed securities - Commercial mortgage-backed securities
Schedule of Available-for-sale Securities
Amortized Cost	325,071	354,418
Gross Unrealized Gains	3,132	268
Gross Unrealized Losses	(1,216)	(3,024)
Available-for-sale investment securities, at fair value	326,987	351,662
U.S. government agency and U.S. government sponsored enterprise mortgage-backed securities - Residential mortgage-backed securities
Schedule of Available-for-sale Securities
Amortized Cost	927,989	996,255
Gross Unrealized Gains	9,421	7,542
Gross Unrealized Losses	(2,311)	(6,401)
Available-for-sale investment securities, at fair value	935,099	997,396
Municipal securities
Schedule of Available-for-sale Securities
Amortized Cost	156,327	173,785
Gross Unrealized Gains	3,254	2,657
Gross Unrealized Losses	(155)	(793)
Available-for-sale investment securities, at fair value	159,426	175,649
Non-agency residential mortgage-backed securities \| Investment grade
Schedule of Available-for-sale Securities
Amortized Cost	58,960	62,133
Gross Unrealized Gains	1,015	433
Gross Unrealized Losses	(76)	(173)
Available-for-sale investment securities, at fair value	59,899	62,393
Corporate debt securities \| Investment grade
Schedule of Available-for-sale Securities
Amortized Cost	368,206	366,921
Gross Unrealized Gains	212	132
Gross Unrealized Losses	(2,513)	(2,340)
Available-for-sale investment securities, at fair value	365,905	364,713
Corporate debt securities \| Non-investment grade
Schedule of Available-for-sale Securities
Amortized Cost	10,191	11,491
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(2,267)	(1,849)
Available-for-sale investment securities, at fair value	7,924	9,642
Other securities
Schedule of Available-for-sale Securities
Amortized Cost	44,136	44,664
Gross Unrealized Gains	499	124
Gross Unrealized Losses	(327)	(381)
Available-for-sale investment securities, at fair value	44,308	$ 44,407
Non-agency commercial mortgage-backed security
Schedule of Held-to-maturity Securities
Amortized Cost	160,135
Gross Unrealized Gains	0
Gross Unrealized Losses	0
Fair Value	$ 160,135

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