INVESTMENT SECURITIES - Fair value of impaired investment securities (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Mar. 31, 2020
Debt Securities, Available-for-sale [Line Items]
Less than 12 months, Estimated Fair Value	$ 31	$ 16,233
Less than 12 months, Unrealized Losses		(90)
12 months or longer, Estimated Fair Value	6,534	5,320
12 months or longer, Unrealized Losses	(90)	(101)
Total, Estimated Fair Value	6,565	21,553
Total, Unrealized Losses	(90)	(191)
Agency securities
Debt Securities, Available-for-sale [Line Items]
Less than 12 months, Estimated Fair Value		1,998
Less than 12 months, Unrealized Losses		(10)
12 months or longer, Estimated Fair Value	1,998
12 months or longer, Unrealized Losses	(8)
Total, Estimated Fair Value	1,998	1,998
Total, Unrealized Losses	(8)	(10)
Real estate mortgage investment conduits
Debt Securities, Available-for-sale [Line Items]
Less than 12 months, Estimated Fair Value	31
Total, Estimated Fair Value	31
Residential mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Less than 12 months, Estimated Fair Value		2,509
Less than 12 months, Unrealized Losses		(22)
12 months or longer, Estimated Fair Value		409
12 months or longer, Unrealized Losses		(8)
Total, Estimated Fair Value		2,918
Total, Unrealized Losses		(30)
Other mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Less than 12 months, Estimated Fair Value		11,726
Less than 12 months, Unrealized Losses		(58)
12 months or longer, Estimated Fair Value	4,536	4,911
12 months or longer, Unrealized Losses	(82)	(93)
Total, Estimated Fair Value	4,536	16,637
Total, Unrealized Losses	$ (82)	$ (151)

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for more than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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