INVESTMENT SECURITIES - Summary of Amortized Cost and Fair Value (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Amortized Cost	$ 1,287,846	$ 1,220,444
Gross Unrealized Gains	21,303	20,959
Gross Unrealized Losses	(5,781)	(9,972)
Securities available-for-sale, at fair value	1,303,368	1,231,431
SBA loan pool securities
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Amortized Cost	15,489	17,436
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(68)	(82)
Securities available-for-sale, at fair value	15,421	17,354
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	190,708	99,591
Gross Unrealized Gains	3,556	6,793
Gross Unrealized Losses	(978)	0
Securities available-for-sale, at fair value	193,286	106,384
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	254,775	209,426
Gross Unrealized Gains	2,062	2,571
Gross Unrealized Losses	(1,532)	(166)
Securities available-for-sale, at fair value	255,305	211,831
Municipal securities
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Amortized Cost	117,955	64,355
Gross Unrealized Gains	3,167	4,272
Gross Unrealized Losses	(705)	(4)
Securities available-for-sale, at fair value	120,417	68,623
Non-agency residential mortgage-backed securities
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Amortized Cost	149	156
Gross Unrealized Gains	5	4
Gross Unrealized Losses	0	0
Securities available-for-sale, at fair value	154	160
Collateralized loan obligations
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Amortized Cost	551,775	687,505
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(2,498)	(9,720)
Securities available-for-sale, at fair value	549,277	677,785
Corporate debt securities
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Amortized Cost	156,995	141,975
Gross Unrealized Gains	12,513	7,319
Gross Unrealized Losses	0	0
Securities available-for-sale, at fair value	$ 169,508	$ 149,294

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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-Topic 320
-SubTopic 10
-Section 50
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Amount, before tax, of unrealized loss 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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Amortized cost excluding accrued interest, before allowance for credit loss, of 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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-Publisher FASB
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Amount excluding accrued interest, of 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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