Condensed Financial Statements of Greene County Bancorp, Inc., Condensed Statements of Cash Flows (Details) - USD ($) $ in Thousands	12 Months Ended
	Jun. 30, 2022	Jun. 30, 2021
Cash flows from operating activities [Abstract]
Net Income	$ 27,986	$ 23,942
Adjustments to reconcile net income to cash provided by operating activities [Abstract]
Amortization of subordinated debt issuance costs	165	67
Net decrease in prepaid expenses and other assets	176	(934)
Net cash provided by operating activities	35,354	27,753
Cash flows from Investing Activities [Abstract]
Net cash used in investing activities	(471,183)	(417,137)
Cash flows from financing activities [Abstract]
Net decrease in short-term advances - other banks	(3,000)	(14,884)
Net proceeds from subordinated notes payable	29,501	19,577
Payment of cash dividends	(2,634)	(2,430)
Net cash provided by financing activities	355,063	498,696
Net (decrease) increase in cash and cash equivalents	(80,766)	109,312
Parent Company [Member]
Cash flows from operating activities [Abstract]
Net Income	27,986	23,942
Adjustments to reconcile net income to cash provided by operating activities [Abstract]
Undistributed earnings of subsidiaries	(28,155)	(20,362)
Amortization of subordinated debt issuance costs	165	68
Net decrease in prepaid expenses and other assets	18	4
Net decrease (increase) in dividend receivable	1,500	(1,500)
Net increase in total liabilities	231	275
Net cash provided by operating activities	1,745	2,427
Cash flows from Investing Activities [Abstract]
Investment in subsidiary	(7,000)	(17,500)
Net cash used in investing activities	(7,000)	(17,500)
Cash flows from financing activities [Abstract]
Net decrease in short-term advances - other banks	(3,000)	(4,000)
Net proceeds from subordinated notes payable	29,501	19,577
Payment of cash dividends	(2,634)	(2,430)
Net cash provided by financing activities	23,867	13,147
Net (decrease) increase in cash and cash equivalents	18,612	(1,926)
Cash and cash equivalents at beginning of year	279	2,205
Cash and cash equivalents at end of year	$ 18,891	$ 279