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Loans - Summary of the balances of loans (Details) - USD ($) $ in Thousands	Mar. 31, 2026	Dec. 31, 2025	Jun. 30, 2025	Mar. 31, 2025	Dec. 31, 2024	Jun. 30, 2024
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	$ 843,537		$ 754,110
Allowance for credit losses	(4,537)	$ (4,396)	(4,151)	$ (3,600)	$ (3,635)	$ (3,451)
Net deferred loan origination costs	1,544		1,261
Loans, net	840,544		751,220
Mortgage loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	839,177		749,436
Mortgage loans \| Residential real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	389,485		357,748
Mortgage loans \| Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	108,515		102,270
Mortgage loans \| Multi - family
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	216,340		166,691
Mortgage loans \| Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	95,803		95,941
Mortgage loans \| Home equity loans and lines-of-credit
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	29,034		26,786
Commercial loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	4,127		4,335
Allowance for credit losses	(39)	(37)	(298)	(29)	(76)	(39)
Consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	233		339
Allowance for credit losses	$ (1)	$ (1)	$ (2)	$ (2)	$ (5)	$ (9)