Condensed Financial Statements of Greene County Bancorp, Inc., Condensed Statements of Financial Condition (Details) - USD ($) $ in Thousands	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2020
ASSETS [Abstract]
Prepaid expenses and other assets	$ 15,237	$ 8,451
Total assets	2,571,740	2,200,335
LIABILITIES AND SHAREHOLDERS' EQUITY [Abstract]
Borrowings from other banks, short-term	0	3,000
Subordinated notes payable, net	49,310	19,644
Accrued expenses and other liabilities	28,412	22,999
Total liabilities	2,414,026	2,050,751
Total shareholders' equity	157,714	149,584	$ 128,805
Total liabilities and shareholders' equity	2,571,740	2,200,335
Parent Company [Member]
ASSETS [Abstract]
Cash and cash equivalents	18,891	279	$ 2,205
Investment in subsidiaries	188,638	170,705
Dividend receivable	0	1,500
Prepaid expenses and other assets	90	108
Total assets	207,619	172,592
LIABILITIES AND SHAREHOLDERS' EQUITY [Abstract]
Borrowings from other banks, short-term	0	3,000
Subordinated notes payable, net	49,310	19,644
Accrued expenses and other liabilities	595	364
Total liabilities	49,905	23,008
Total shareholders' equity	157,714	149,584
Total liabilities and shareholders' equity	$ 207,619	$ 172,592