Condensed Financial Statements of Greene County Bancorp, Inc., Condensed Statements of Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
OPERATING EXPENSES [Abstract]
Interest on borrowings	$ 962	$ 240
Other	2,820	2,619
Net income	23,942	18,727
Parent Company [Member]
INCOME [Abstract]
Equity in undistributed net income of subsidiaries	20,362	15,817
Dividend distributed by subsidiary	4,834	3,254
Interest-earning deposits	5	10
Total Income	25,201	19,081
OPERATING EXPENSES [Abstract]
Legal fees	78	49
Interest on borrowings	820	7
Other	361	298
Total operating expenses	1,259	354
Net income	$ 23,942	$ 18,727