Condensed Financial Statements of Greene County Bancorp, Inc., Condensed Statements of Financial Condition (Details) - USD ($) $ in Thousands	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2022
ASSETS [Abstract]
Long-term certificates of deposit	$ 2,831	$ 4,576
Securities available-for-sale, at fair value	350,001	281,133
Accrued interest receivable	14,269	12,249
Prepaid expenses and other assets	17,230	17,482
Total assets	2,825,788	2,698,283
LIABILITIES AND SHAREHOLDERS' EQUITY [Abstract]
Subordinated notes payable, net	49,681	49,495
Accrued expenses and other liabilities	31,429	28,344
Total liabilities	2,619,788	2,515,000
Total shareholders' equity	206,000	183,283	$ 157,714
Total liabilities and shareholders' equity	2,825,788	2,698,283
Parent Company [Member]
ASSETS [Abstract]
Cash and cash equivalents	22,469	19,822	$ 18,891
Investment in subsidiaries	233,758	208,861
Long-term certificates of deposit	0	3,826
Securities available-for-sale, at fair value	0	761
Accrued interest receivable	0	26
Prepaid expenses and other assets	38	93
Total assets	256,265	233,389
LIABILITIES AND SHAREHOLDERS' EQUITY [Abstract]
Subordinated notes payable, net	49,681	49,495
Accrued expenses and other liabilities	584	611
Total liabilities	50,265	50,106
Total shareholders' equity	206,000	183,283
Total liabilities and shareholders' equity	$ 256,265	$ 233,389