INVESTMENT SECURITIES - Summary of Amortized Cost and Fair Value (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Amortized Cost	$ 1,244,070	$ 929,449
Gross Unrealized Gains	19,868	151
Gross Unrealized Losses	(18,071)	(17,020)
Securities available-for-sale, at fair value	1,245,867	912,580
Less Than 12 Months	116,475	190,527
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(1,025)	(2,223)
12 Months or Longer	621,559	668,808
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(17,046)	(14,797)
Debt Securities, Available-for-sale, Unrealized Loss Position	738,034	859,335
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	(18,071)	(17,020)
SBA loan pool securities
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Amortized Cost	17,853
Gross Unrealized Gains	3
Gross Unrealized Losses	(49)
Securities available-for-sale, at fair value	17,807
Less Than 12 Months	13,351
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(49)
12 Months or Longer	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0
Debt Securities, Available-for-sale, Unrealized Loss Position	13,351
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	(49)
U.S. government agency and U.S. government sponsored enterprise residential mortgage-backed securities
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Amortized Cost	99,862	37,613
Gross Unrealized Gains	7,569	0
Gross Unrealized Losses	0	(1,157)
Securities available-for-sale, at fair value	107,431	36,456
Less Than 12 Months	10,153	35,872
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(36)	(1,157)
12 Months or Longer	0	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	0
Debt Securities, Available-for-sale, Unrealized Loss Position	10,153	35,872
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	(36)	(1,157)
U.S. government agency and U.S. government sponsored enterprise collateralized mortgage obligations
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Amortized Cost	216,250	91,543
Gross Unrealized Gains	2,182	16
Gross Unrealized Losses	(36)	(260)
Securities available-for-sale, at fair value	218,396	91,299
Less Than 12 Months		73,379
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss		(260)
12 Months or Longer		0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss		0
Debt Securities, Available-for-sale, Unrealized Loss Position		73,379
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss		(260)
Municipal securities
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Amortized Cost	64,373	52,997
Gross Unrealized Gains	4,890	51
Gross Unrealized Losses	(30)	(359)
Securities available-for-sale, at fair value	69,233	52,689
Less Than 12 Months	11,381	31,723
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(30)	(359)
12 Months or Longer	0	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	0
Debt Securities, Available-for-sale, Unrealized Loss Position	11,381	31,723
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	(30)	(359)
Non-agency residential mortgage-backed securities
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Amortized Cost	159	191
Gross Unrealized Gains	4	5
Gross Unrealized Losses	0	0
Securities available-for-sale, at fair value	163	196
Collateralized loan obligations
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Amortized Cost	703,605	733,605
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(17,674)	(15,244)
Securities available-for-sale, at fair value	685,931	718,361
Less Than 12 Months	64,372	49,553
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(628)	(447)
12 Months or Longer	621,559	668,808
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(17,046)	(14,797)
Debt Securities, Available-for-sale, Unrealized Loss Position	685,931	718,361
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	(17,674)	(15,244)
Corporate debt securities
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Amortized Cost	141,968	13,500
Gross Unrealized Gains	5,220	79
Gross Unrealized Losses	(282)	0
Securities available-for-sale, at fair value	146,906	$ 13,579
Less Than 12 Months	17,218
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(282)
12 Months or Longer	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0
Debt Securities, Available-for-sale, Unrealized Loss Position	17,218
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	$ (282)

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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