INVESTMENT SECURITIES - Summary of Amortized Cost and Fair Value (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Securities held-to-maturity:
Amortized Cost	$ 0	$ 884,234
Gross Unrealized Gains		17,442
Gross Unrealized Losses		(1,933)
Fair Value		899,743
Securities available-for-sale:
Amortized Cost	2,742,297	2,396,968
Gross Unrealized Gains	28,008	12,958
Gross Unrealized Losses	(14,641)	(28,438)
Fair Value	2,755,664	2,381,488
SBA loan pool securities
Securities available-for-sale:
Amortized Cost	1,056	1,221
Gross Unrealized Gains	9	0
Gross Unrealized Losses	0	0
Fair Value	1,065	1,221
U.S. government agency and U.S. government sponsored enterprise residential mortgage-backed securities
Securities available-for-sale:
Amortized Cost	503,193	830,682
Gross Unrealized Gains	20	9
Gross Unrealized Losses	(14,096)	(23,418)
Fair Value	489,117	807,273
Non-agency residential mortgage-backed securities
Securities available-for-sale:
Amortized Cost	844	121,397
Gross Unrealized Gains	16	18
Gross Unrealized Losses	(1)	(4,238)
Fair Value	859	117,177
Non-agency commercial mortgage-backed securities
Securities available-for-sale:
Amortized Cost	305,360
Gross Unrealized Gains	5,737
Gross Unrealized Losses	(180)
Fair Value	310,917
Collateralized loan obligations
Securities available-for-sale:
Amortized Cost	1,808,126	1,395,094
Gross Unrealized Gains	11,429	12,449
Gross Unrealized Losses	(364)	(674)
Fair Value	1,819,191	1,406,869
Corporate debt securities
Securities available-for-sale:
Amortized Cost	123,718	48,574
Gross Unrealized Gains	10,797	482
Gross Unrealized Losses	0	(108)
Fair Value	$ 134,515	48,948
Non-agency commercial mortgage-backed securities
Securities held-to-maturity:
Amortized Cost		305,918
Gross Unrealized Gains		2,949
Gross Unrealized Losses		(1,781)
Fair Value		307,086
Collateralized loan obligations
Securities held-to-maturity:
Amortized Cost		338,226
Gross Unrealized Gains		1,461
Gross Unrealized Losses		(61)
Fair Value		339,626
Corporate debt securities
Securities held-to-maturity:
Amortized Cost		240,090
Gross Unrealized Gains		13,032
Gross Unrealized Losses		(91)
Fair Value		$ 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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