SECURITIES - Amortized cost and Fair values of securities with gross unrealized gains and losses (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022	Mar. 31, 2022
Available-for-sale:
Amortized Cost	$ 831,624	$ 934,456
Gross Unrealized Gains	99	106
Gross Unrealized Losses	(72,262)	(91,038)
Allowance for Credit Losses	0
Fair Value	759,461	843,524
Held-to-maturity
Amortized Cost	521,439	541,600	$ 114,850
Gross Unrealized Gains	394	195
Gross Unrealized Losses	(55,337)	(62,994)
Fair Value	466,496	478,801	104,131
Allowance for Credit Losses	0
U.S. Treasury
Available-for-sale:
Amortized Cost	159,715	169,860
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(11,093)	(15,345)
Allowance for Credit Losses	0
Fair Value	148,622	154,515
U.S. government agency
Available-for-sale:
Amortized Cost	55,359	59,291
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(3,262)	(4,134)
Allowance for Credit Losses	0
Fair Value	52,097	55,157
Held-to-maturity
Amortized Cost	88,448	88,424	78,841
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(8,292)	(9,728)
Fair Value	80,156	78,696	71,048
Allowance for Credit Losses	0
Municipal
Available-for-sale:
Amortized Cost	229,030	275,972
Gross Unrealized Gains	26	46
Gross Unrealized Losses	(23,499)	(32,189)
Allowance for Credit Losses	0
Fair Value	205,557	243,829
Held-to-maturity
Amortized Cost	38,442	42,167
Gross Unrealized Gains	394	195
Gross Unrealized Losses	(163)	(314)
Fair Value	38,673	42,048
Allowance for Credit Losses	0
Agency residential
Available-for-sale:
Amortized Cost	188,641	213,676
Gross Unrealized Gains	61	5
Gross Unrealized Losses	(14,718)	(18,240)
Allowance for Credit Losses	0
Fair Value	173,984	195,441
Held-to-maturity
Amortized Cost	95,828	102,728	8,175
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(5,569)	(6,470)
Fair Value	90,259	96,258	7,651
Allowance for Credit Losses	0
Agency commercial
Available-for-sale:
Amortized Cost	141,214	150,060
Gross Unrealized Gains	3	0
Gross Unrealized Losses	(14,205)	(17,172)
Allowance for Credit Losses	0
Fair Value	127,012	132,888
Held-to-maturity
Amortized Cost	298,721	308,281	27,834
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(41,313)	(46,482)
Fair Value	257,408	261,799	$ 25,432
Allowance for Credit Losses	0
Corporate
Available-for-sale:
Amortized Cost	57,665	65,597
Gross Unrealized Gains	9	55
Gross Unrealized Losses	(5,485)	(3,958)
Allowance for Credit Losses	0
Fair Value	$ 52,189	$ 61,694

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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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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Amount excluding accrued interest, of allowance for credit loss 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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Amount of accumulated unrecognized gain on investment in debt security measured at amortized cost (held-to-maturity).

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Fair value of investment in debt security measured at amortized cost (held-to-maturity).

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