Condensed Financial Statements of Greene County Bancorp, Inc., Condensed Statements of Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
OPERATING EXPENSES [Abstract]
Other	$ 2,743	$ 2,349
Net income	17,484	14,408
Parent Company [Member]
INCOME [Abstract]
Equity in undistributed net income of subsidiaries	14,770	12,812
Dividend distributed by subsidiary	3,084	1,914
Interest-earning deposits	3	2
Total Income	17,857	14,728
OPERATING EXPENSES [Abstract]
Legal fees	48	56
Other	325	264
Total operating expenses	373	320
Net income	$ 17,484	$ 14,408