FAIR VALUE MEASUREMENTS - Estimated Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Sep. 30, 2025	Mar. 31, 2025
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Transfers of assets from level 1 to level 2	$ 0	$ 0
Transfers of assets from level 2 to level 1	0	0
Transfers of assets into level 3	0	0
Transfers of assets out of level 3	0	0
Recurring basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets measured at fair value on a recurring basis	118,447	119,436
Recurring basis \| Municipal securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets measured at fair value on a recurring basis	31,841	31,019
Recurring basis \| Agency securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets measured at fair value on a recurring basis	30,934	30,203
Recurring basis \| Real estate mortgage investment conduits
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets measured at fair value on a recurring basis	22,890	23,490
Recurring basis \| Residential mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets measured at fair value on a recurring basis	9,169	10,226
Recurring basis \| Other mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets measured at fair value on a recurring basis	23,613	24,498
Recurring basis \| Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets measured at fair value on a recurring basis	118,447	119,436
Recurring basis \| Level 2 \| Municipal securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets measured at fair value on a recurring basis	31,841	31,019
Recurring basis \| Level 2 \| Agency securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets measured at fair value on a recurring basis	30,934	30,203
Recurring basis \| Level 2 \| Real estate mortgage investment conduits
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets measured at fair value on a recurring basis	22,890	23,490
Recurring basis \| Level 2 \| Residential mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets measured at fair value on a recurring basis	9,169	10,226
Recurring basis \| Level 2 \| Other mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets measured at fair value on a recurring basis	$ 23,613	$ 24,498

RIVERVIEW BANCORP INC 10-Q