AVAILABLE-FOR-SALE INVESTMENT SECURITIES (Details) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Schedule of Available-for-sale Investment Securities
Amortized Cost	$ 2,937,313	$ 2,619,307
Gross Unrealized Gains	23,056	21,278
Gross Unrealized Losses	(8,092)	(13,968)
Available-for-sale investment securities, at fair value	2,952,277	2,626,617
U.S. Treasury securities
Schedule of Available-for-sale Investment Securities
Amortized Cost	750,032	873,101
Gross Unrealized Gains	2,581	1,971
Gross Unrealized Losses	(8)	(1,637)
Available-for-sale investment securities, at fair value	752,605	873,435
U.S. government agency and U.S. government sponsored enterprise debt securities
Schedule of Available-for-sale Investment Securities
Amortized Cost	701,919	311,927
Gross Unrealized Gains	1,544	490
Gross Unrealized Losses	(1,619)	(1,393)
Available-for-sale investment securities, at fair value	701,844	311,024
U.S. government agency and U.S. government sponsored enterprise mortgage-backed securities - Commercial mortgage-backed securities
Schedule of Available-for-sale Investment Securities
Amortized Cost	271,171	140,957
Gross Unrealized Gains	2,584	1,056
Gross Unrealized Losses	(405)	(593)
Available-for-sale investment securities, at fair value	273,350	141,420
U.S. government agency and U.S. government sponsored enterprise mortgage-backed securities - Residential mortgage-backed securities
Schedule of Available-for-sale Investment Securities
Amortized Cost	746,632	785,412
Gross Unrealized Gains	10,081	9,754
Gross Unrealized Losses	(1,815)	(4,078)
Available-for-sale investment securities, at fair value	754,898	791,088
Municipal securities
Schedule of Available-for-sale Investment Securities
Amortized Cost	203,832	245,408
Gross Unrealized Gains	4,604	6,202
Gross Unrealized Losses	(1,611)	(1,162)
Available-for-sale investment securities, at fair value	206,825	250,448
Other residential mortgage-backed securities \| Investment grade
Schedule of Available-for-sale Investment Securities
Amortized Cost	65,706	52,694
Gross Unrealized Gains	947	1,359
Gross Unrealized Losses	(116)	(135)
Available-for-sale investment securities, at fair value	66,537	53,918
Other commercial mortgage-backed securities \| Investment grade
Schedule of Available-for-sale Investment Securities
Amortized Cost		34,000
Gross Unrealized Gains		53
Gross Unrealized Losses		0
Available-for-sale investment securities, at fair value		34,053
Corporate debt securities \| Investment grade
Schedule of Available-for-sale Investment Securities
Amortized Cost	142,216	116,236
Gross Unrealized Gains	22	0
Gross Unrealized Losses	(1,112)	(1,054)
Available-for-sale investment securities, at fair value	141,126	115,182
Corporate debt securities \| Non-investment grade
Schedule of Available-for-sale Investment Securities
Amortized Cost	11,525	17,881
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(1,001)	(3,200)
Available-for-sale investment securities, at fair value	10,524	14,681
Other securities
Schedule of Available-for-sale Investment Securities
Amortized Cost	44,280	41,691
Gross Unrealized Gains	693	393
Gross Unrealized Losses	(405)	(716)
Available-for-sale investment securities, at fair value	$ 44,568	$ 41,368

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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