Loans - Activity in the allowance for credit losses by portfolio segment (Details) - USD ($)	3 Months Ended		9 Months Ended
	Mar. 31, 2025	Mar. 31, 2024	Mar. 31, 2025	Mar. 31, 2024
Activity in the allowance for credit losses - loans by loan class
Balance at beginning of year	$ 1,651,000	$ 1,891,000	$ 1,797,116	$ 2,159,000
Recoveries	3,000	1,000	4,000	2,000
Provision for (Recovery of) Credit Losses-Loans	(42,000)	(122,000)	(189,000)	(216,000)
Balance at end of period	1,612,332	1,770,000	1,612,332	1,770,000
Cumulative effect of accounting change
Activity in the allowance for credit losses - loans by loan class
Balance at beginning of year				(175,000)
Consumer
Activity in the allowance for credit losses - loans by loan class
Balance at beginning of year	9,000		5,000	2,000
Recoveries			1,000	2,000
Provision for (Recovery of) Credit Losses-Loans			3,000	(10,000)
Balance at end of period	9,000	5,000	9,000	5,000
Consumer \| Cumulative effect of accounting change
Activity in the allowance for credit losses - loans by loan class
Balance at beginning of year				11,000
Commercial real estate \| Commercial real estate
Activity in the allowance for credit losses - loans by loan class
Balance at beginning of year	262,000	344,000	259,000	1,196,000
Provision for (Recovery of) Credit Losses-Loans	43,000	(41,000)	46,000	(75,000)
Balance at end of period	305,000	303,000	305,000	303,000
Commercial real estate \| Commercial real estate \| Cumulative effect of accounting change
Activity in the allowance for credit losses - loans by loan class
Balance at beginning of year				(818,000)
Commercial \| Commercial and industrial
Activity in the allowance for credit losses - loans by loan class
Balance at beginning of year	14,000	21,000	16,000	18,000
Provision for (Recovery of) Credit Losses-Loans	(2,000)	(3,000)	(4,000)	(5,000)
Balance at end of period	12,000	18,000	12,000	18,000
Commercial \| Commercial and industrial \| Cumulative effect of accounting change
Activity in the allowance for credit losses - loans by loan class
Balance at beginning of year				5,000
Commercial \| Construction
Activity in the allowance for credit losses - loans by loan class
Balance at beginning of year		6,000	28,000	6,000
Provision for (Recovery of) Credit Losses-Loans	22,000	(1,000)	(6,000)	(3,000)
Balance at end of period	22,000	5,000	22,000	5,000
Commercial \| Construction \| Cumulative effect of accounting change
Activity in the allowance for credit losses - loans by loan class
Balance at beginning of year				2,000
Residential \| One-to-four-family residential
Activity in the allowance for credit losses - loans by loan class
Balance at beginning of year	1,209,000	1,295,000	1,314,000	207,000
Recoveries	3,000		3,000
Provision for (Recovery of) Credit Losses-Loans	(96,000)	(42,000)	(201,000)	(91,000)
Balance at end of period	1,116,000	1,253,000	1,116,000	1,253,000
Residential \| One-to-four-family residential \| Cumulative effect of accounting change
Activity in the allowance for credit losses - loans by loan class
Balance at beginning of year				1,137,000
Residential \| Multi-family real estate
Activity in the allowance for credit losses - loans by loan class
Balance at beginning of year	157,000	218,000	175,000	365,000
Provision for (Recovery of) Credit Losses-Loans	(9,000)	(32,000)	(27,000)	(32,000)
Balance at end of period	$ 148,000	186,000	$ 148,000	186,000
Residential \| Multi-family real estate \| Cumulative effect of accounting change
Activity in the allowance for credit losses - loans by loan class
Balance at beginning of year				(147,000)
Consumer Loans
Activity in the allowance for credit losses - loans by loan class
Balance at beginning of year		7,000
Recoveries		1,000
Provision for (Recovery of) Credit Losses-Loans		(3,000)
Balance at end of period		$ 5,000		5,000
Unallocated
Activity in the allowance for credit losses - loans by loan class
Balance at beginning of year				365,000
Unallocated \| Cumulative effect of accounting change
Activity in the allowance for credit losses - loans by loan class
Balance at beginning of year				$ (365,000)

Marathon Bancorp, Inc. /MD/ 10-Q