Condensed Financial Statements of Greene County Bancorp, Inc., Condensed Statements of Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
OPERATING EXPENSES [Abstract]
Other	$ 2,619	$ 2,743
Net income	18,727	17,484
Parent Company [Member]
INCOME [Abstract]
Equity in undistributed net income of subsidiaries	15,817	14,770
Dividend distributed by subsidiary	3,254	3,084
Interest-earning deposits	10	3
Total Income	19,081	17,857
OPERATING EXPENSES [Abstract]
Legal fees	49	48
Other	305	325
Total operating expenses	354	373
Net income	$ 18,727	$ 17,484