INVESTMENT SECURITIES - Fair value of impaired investment securities (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Mar. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Less than 12 months, Estimated Fair Value	$ 16,233	$ 0
Less than 12 months, Unrealized Losses	(90)	0
12 months or longer, Estimated Fair Value	5,320	168,238
12 months or longer, Unrealized Losses	(101)	(3,526)
Total, Estimated Fair Value	21,553	168,238
Total, Unrealized Losses	(191)	(3,526)
Municipal securities
Debt Securities, Available-for-sale [Line Items]
Less than 12 months, Estimated Fair Value		0
Less than 12 months, Unrealized Losses		0
12 months or longer, Estimated Fair Value		6,554
12 months or longer, Unrealized Losses		(34)
Total, Estimated Fair Value		6,554
Total, Unrealized Losses		(34)
Agency securities
Debt Securities, Available-for-sale [Line Items]
Less than 12 months, Estimated Fair Value	1,998	0
Less than 12 months, Unrealized Losses	(10)	0
12 months or longer, Estimated Fair Value	0	6,861
12 months or longer, Unrealized Losses	0	(107)
Total, Estimated Fair Value	1,998	6,861
Total, Unrealized Losses	(10)	(107)
Real estate mortgage investment conduits
Debt Securities, Available-for-sale [Line Items]
Less than 12 months, Estimated Fair Value		0
Less than 12 months, Unrealized Losses		0
12 months or longer, Estimated Fair Value		40,126
12 months or longer, Unrealized Losses		(673)
Total, Estimated Fair Value		40,126
Total, Unrealized Losses		(673)
Residential mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Less than 12 months, Estimated Fair Value	2,509	0
Less than 12 months, Unrealized Losses	(22)	0
12 months or longer, Estimated Fair Value	409	74,288
12 months or longer, Unrealized Losses	(8)	(1,588)
Total, Estimated Fair Value	2,918	74,288
Total, Unrealized Losses	(30)	(1,588)
Other mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Less than 12 months, Estimated Fair Value	11,726	0
Less than 12 months, Unrealized Losses	(58)	0
12 months or longer, Estimated Fair Value	4,911	40,409
12 months or longer, Unrealized Losses	(93)	(1,124)
Total, Estimated Fair Value	16,637	40,409
Total, Unrealized Losses	$ (151)	$ (1,124)

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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