INVESTMENT SECURITIES - Summary of Amortized Cost and Fair Value (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Securities held-to-maturity:
Amortized Cost	$ 0	$ 884,234
Gross Unrealized Gains		17,442
Gross Unrealized Losses		(1,933)
Securities held-to-maturity	0	899,743
Securities available-for-sale:
Amortized Cost	2,567,393	2,396,968
Gross Unrealized Gains	23,679	12,958
Gross Unrealized Losses	(15,603)	(28,438)
Fair Value	2,575,469	2,381,488
SBA loan pool securities
Securities available-for-sale:
Amortized Cost	1,056	1,221
Gross Unrealized Gains	2	0
Gross Unrealized Losses	0	0
Fair Value	1,058	1,221
U.S. government agency and U.S. government sponsored enterprise residential mortgage-backed securities
Securities available-for-sale:
Amortized Cost	492,255	830,682
Gross Unrealized Gains	10	9
Gross Unrealized Losses	(15,336)	(23,418)
Fair Value	476,929	807,273
Non-agency residential mortgage-backed securities
Securities available-for-sale:
Amortized Cost	741	121,397
Gross Unrealized Gains	16	18
Gross Unrealized Losses	(1)	(4,238)
Fair Value	756	117,177
Non-agency commercial mortgage-backed securities
Securities available-for-sale:
Amortized Cost	305,172
Gross Unrealized Gains	5,339
Gross Unrealized Losses	0
Fair Value	310,511
Collateralized loan obligations
Securities available-for-sale:
Amortized Cost	1,691,455	1,395,094
Gross Unrealized Gains	11,129	12,449
Gross Unrealized Losses	(266)	(674)
Fair Value	1,702,318	1,406,869
Corporate debt securities
Securities available-for-sale:
Amortized Cost	76,714	48,574
Gross Unrealized Gains	7,183	482
Gross Unrealized Losses	0	(108)
Fair Value	$ 83,897	48,948
Corporate debt securities
Securities held-to-maturity:
Amortized Cost		305,918
Gross Unrealized Gains		2,949
Gross Unrealized Losses		(1,781)
Securities held-to-maturity		307,086
Collateralized loan obligations
Securities held-to-maturity:
Amortized Cost		338,226
Gross Unrealized Gains		1,461
Gross Unrealized Losses		(61)
Securities held-to-maturity		339,626
Non-agency commercial mortgage-backed securities
Securities held-to-maturity:
Amortized Cost		240,090
Gross Unrealized Gains		13,032
Gross Unrealized Losses		(91)
Securities held-to-maturity		$ 253,031

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

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Amount after other than temporary impairment (OTTI) accretion, of investments in debt securities classified as held-to-maturity.

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