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INVESTMENT SECURITIES - Unrealized Gain/Loss on Investment (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
AFS
Amortized cost	$ 1,439,449	$ 1,509,736
Gross unrealized gains	154	135
Gross unrealized losses	(168,949)	(131,097)
Fair value	1,270,654	1,378,774
Residential mortgage-backed securities
AFS
Amortized cost	198,589	207,445
Gross unrealized gains	48	0
Gross unrealized losses	(15,668)	(10,183)
Fair value	182,969	197,262
Commercial mortgage-backed securities
AFS
Amortized cost	57,481	65,411
Gross unrealized gains	0	0
Gross unrealized losses	(9,918)	(9,362)
Fair value	47,563	56,049
Residential collateralized mortgage obligations
AFS
Amortized cost	526,683	592,449
Gross unrealized gains	0	12
Gross unrealized losses	(47,127)	(39,422)
Fair value	479,556	553,039
Commercial collateralized mortgage obligations
AFS
Amortized cost	65,686	77,909
Gross unrealized gains	0	0
Gross unrealized losses	(6,934)	(7,390)
Fair value	58,752	70,519
Municipal bonds
AFS
Amortized cost	455,467	469,346
Gross unrealized gains	106	41
Gross unrealized losses	(77,275)	(57,839)
Fair value	378,298	411,548
HTM
Amortized cost	2,389	2,441
Gross unrealized gains	0	0
Gross unrealized losses	(96)	(56)
Fair value	2,293	2,385
Corporate debt securities
AFS
Amortized cost	45,664	46,672
Gross unrealized gains	0	74
Gross unrealized losses	(6,696)	(3,801)
Fair value	38,968	42,945
U.S. Treasury securities
AFS
Amortized cost	22,746	23,005
Gross unrealized gains	0	0
Gross unrealized losses	(3,301)	(3,071)
Fair value	19,445	19,934
Agency debentures
AFS
Amortized cost	67,133	27,499
Gross unrealized gains	0	8
Gross unrealized losses	(2,030)	(29)
Fair value	$ 65,103	$ 27,478

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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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