Condensed Financial Statements of Greene County Bancorp, Inc., Condensed Statements of Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
OPERATING EXPENSES [Abstract]
Other	$ 2,038	$ 2,244
Net income	11,187	8,963
Parent Company [Member]
INCOME [Abstract]
Equity in undistributed net income of subsidiaries	9,484	5,239
Dividend distributed by subsidiary	1,904	4,004
Interest-earning deposits	6	6
Total Income	11,394	9,249
OPERATING EXPENSES [Abstract]
Legal fees	46	66
Other	161	220
Total operating expenses	207	286
Net income	$ 11,187	$ 8,963