INVESTMENT SECURITIES - Fair value of impaired investment securities (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Mar. 31, 2023
INVESTMENT SECURITIES
Less than 12 months, Estimated Fair Value	$ 6,963	$ 69,746
Less than 12 months, Unrealized Losses	(180)	(1,500)
12 months or longer, Estimated Fair Value	183,943	134,268
12 months or longer, Unrealized Losses	(31,049)	(22,635)
Total, Estimated Fair Value	190,906	204,014
Total, Unrealized Losses	(31,229)	(24,135)
Debt Securities, Held to maturity
Less than 12 months, estimated fair value	2
12 months or longer, estimated fair value	193,281
12 months or longer, unrealized losses	(42,735)
Total estimated fair value	193,283
Total, unrealized losses	(42,735)
Less than 12 months, Estimated fair value		10,995
Less than 12 months, unrealized losses		(431)
12 months or longer, Estimated Fair Value		199,219
12 months or longer, Unrealized Losses		(33,198)
Total Estimated fair value		210,214
Total, Unrealized Losses		(33,629)
Municipal securities
INVESTMENT SECURITIES
Less than 12 months, Estimated Fair Value	410	6,277
Less than 12 months, Unrealized Losses	(39)	(133)
12 months or longer, Estimated Fair Value	34,866	32,797
12 months or longer, Unrealized Losses	(10,110)	(7,479)
Total, Estimated Fair Value	35,276	39,074
Total, Unrealized Losses	(10,149)	(7,612)
Debt Securities, Held to maturity
12 months or longer, estimated fair value	6,816
12 months or longer, unrealized losses	(3,516)
Total estimated fair value	6,816
Total, unrealized losses	(3,516)
12 months or longer, Estimated Fair Value		7,485
12 months or longer, Unrealized Losses		(2,859)
Total Estimated fair value		7,485
Total, Unrealized Losses		(2,859)
Agency securities
INVESTMENT SECURITIES
Less than 12 months, Estimated Fair Value	5,680	43,451
Less than 12 months, Unrealized Losses	(139)	(747)
12 months or longer, Estimated Fair Value	75,867	36,646
12 months or longer, Unrealized Losses	(7,402)	(5,227)
Total, Estimated Fair Value	81,547	80,097
Total, Unrealized Losses	(7,541)	(5,974)
Debt Securities, Held to maturity
12 months or longer, estimated fair value	47,951
12 months or longer, unrealized losses	(6,080)
Total estimated fair value	47,951
Total, unrealized losses	(6,080)
Less than 12 months, Estimated fair value		8,413
Less than 12 months, unrealized losses		(240)
12 months or longer, Estimated Fair Value		40,437
12 months or longer, Unrealized Losses		(4,851)
Total Estimated fair value		48,850
Total, Unrealized Losses		(5,091)
Real estate mortgage investment conduits
INVESTMENT SECURITIES
Less than 12 months, Estimated Fair Value		2,693
Less than 12 months, Unrealized Losses		(97)
12 months or longer, Estimated Fair Value	25,811	26,184
12 months or longer, Unrealized Losses	(6,940)	(5,273)
Total, Estimated Fair Value	25,811	28,877
Total, Unrealized Losses	(6,940)	(5,370)
Debt Securities, Held to maturity
12 months or longer, estimated fair value	27,130
12 months or longer, unrealized losses	(6,236)
Total estimated fair value	27,130
Total, unrealized losses	(6,236)
Less than 12 months, Estimated fair value		2,580
Less than 12 months, unrealized losses		(191)
12 months or longer, Estimated Fair Value		27,837
12 months or longer, Unrealized Losses		(4,578)
Total Estimated fair value		30,417
Total, Unrealized Losses		(4,769)
Residential mortgage-backed securities
INVESTMENT SECURITIES
Less than 12 months, Estimated Fair Value		3,449
Less than 12 months, Unrealized Losses		(147)
12 months or longer, Estimated Fair Value	13,126	12,022
12 months or longer, Unrealized Losses	(1,439)	(894)
Total, Estimated Fair Value	13,126	15,471
Total, Unrealized Losses	(1,439)	(1,041)
Debt Securities, Held to maturity
Less than 12 months, estimated fair value	2
12 months or longer, estimated fair value	94,933
12 months or longer, unrealized losses	(22,826)
Total estimated fair value	94,935
Total, unrealized losses	(22,826)
Less than 12 months, Estimated fair value		2
12 months or longer, Estimated Fair Value		106,229
12 months or longer, Unrealized Losses		(17,542)
Total Estimated fair value		106,231
Total, Unrealized Losses		(17,542)
Other mortgage-backed securities
INVESTMENT SECURITIES
Less than 12 months, Estimated Fair Value	873	13,876
Less than 12 months, Unrealized Losses	(2)	(376)
12 months or longer, Estimated Fair Value	34,273	26,619
12 months or longer, Unrealized Losses	(5,158)	(3,762)
Total, Estimated Fair Value	35,146	40,495
Total, Unrealized Losses	(5,160)	(4,138)
Debt Securities, Held to maturity
12 months or longer, estimated fair value	16,451
12 months or longer, unrealized losses	(4,077)
Total estimated fair value	16,451
Total, unrealized losses	$ (4,077)
12 months or longer, Estimated Fair Value		17,231
12 months or longer, Unrealized Losses		(3,368)
Total Estimated fair value		17,231
Total, Unrealized Losses		$ (3,368)