INVESTMENT SECURITIES (Details) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities
Amortized Cost	$ 3,220,048	$ 3,783,829
Gross Unrealized Gains	26,645	11,744
Gross Unrealized Losses	(6,361)	(22,347)
Available-for-sale investment securities, at fair value	3,240,332	3,773,226
Schedule of Held-to-maturity Security
Amortized Cost	159,208	0
Fair Value	158,279
Investment Securities
Amortized Cost	3,379,256
Gross Unrealized Gains	26,645
Gross Unrealized Losses	(7,290)
Fair Value	3,398,611
U.S. Treasury securities
Schedule of Available-for-sale Securities
Amortized Cost	485,137	1,002,874
Gross Unrealized Gains	3,423	33
Gross Unrealized Losses	0	(4,392)
Available-for-sale investment securities, at fair value	488,560	998,515
U.S. government agency and U.S. government sponsored enterprise debt securities
Schedule of Available-for-sale Securities
Amortized Cost	701,085	771,288
Gross Unrealized Gains	3,035	555
Gross Unrealized Losses	(191)	(2,994)
Available-for-sale investment securities, at fair value	703,929	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	305,724	354,418
Gross Unrealized Gains	3,443	268
Gross Unrealized Losses	(803)	(3,024)
Available-for-sale investment securities, at fair value	308,364	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	1,050,583	996,255
Gross Unrealized Gains	10,041	7,542
Gross Unrealized Losses	(1,723)	(6,401)
Available-for-sale investment securities, at fair value	1,058,901	997,396
Municipal securities
Schedule of Available-for-sale Securities
Amortized Cost	149,711	173,785
Gross Unrealized Gains	4,246	2,657
Gross Unrealized Losses	(54)	(793)
Available-for-sale investment securities, at fair value	153,903	175,649
Non-agency residential mortgage-backed securities \| Investment grade
Schedule of Available-for-sale Securities
Amortized Cost	54,728	62,133
Gross Unrealized Gains	1,276	433
Gross Unrealized Losses	(29)	(173)
Available-for-sale investment securities, at fair value	55,975	62,393
Corporate debt securities \| Investment grade
Schedule of Available-for-sale Securities
Amortized Cost	418,104	366,921
Gross Unrealized Gains	475	132
Gross Unrealized Losses	(1,715)	(2,340)
Available-for-sale investment securities, at fair value	416,864	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	(1,783)	(1,849)
Available-for-sale investment securities, at fair value	8,408	9,642
Other securities
Schedule of Available-for-sale Securities
Amortized Cost	44,785	44,664
Gross Unrealized Gains	706	124
Gross Unrealized Losses	(63)	(381)
Available-for-sale investment securities, at fair value	45,428	$ 44,407
Non-agency commercial mortgage-backed security
Schedule of Held-to-maturity Security
Amortized Cost	159,208
Gross Unrealized Gains	0
Gross Unrealized Losses	(929)
Fair Value	$ 158,279

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