Condensed Financial Statements of Greene County Bancorp, Inc., Condensed Statements of Comprehensive Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Jun. 30, 2016	Jun. 30, 2015
Condensed Financial Statements, Captions [Line Items]
Net income	$ 8,963	$ 7,189
Other comprehensive income:
Unrealized holding gains on available-for-sale securities, net of income taxes of $328 and $182, respectively	520	288
Accretion of unrealized loss on securities transferred to held-to-maturity, net of income taxes of $6 and $139, respectively	9	220
Pension actuarial loss, net of income tax benefit of ($340) and ($259)	(539)	(409)
Amortization of pension actuarial losses recognized in salaries and benefits, net of income taxes of $52 and $97, respectively	83	153
Total other comprehensive income net of taxes	73	252
Comprehensive income	9,036	7,441
Unrealized holding gains on available-for-sale securities, income taxes	328	182
Accretion of unrealized loss on securities transferred to held-to-maturity, income taxes	6	139
Pension actuarial loss, income tax benefit	(340)	(259)
Amortization of pension actuarial losses recognized in salaries and benefits, income taxes	52	97
Parent Company [Member]
Condensed Financial Statements, Captions [Line Items]
Net income	8,963	7,189
Other comprehensive income:
Unrealized holding gains on available-for-sale securities, net of income taxes of $328 and $182, respectively	520	288
Accretion of unrealized loss on securities transferred to held-to-maturity, net of income taxes of $6 and $139, respectively	9	220
Pension actuarial loss, net of income tax benefit of ($340) and ($259)	(539)	(409)
Amortization of pension actuarial losses recognized in salaries and benefits, net of income taxes of $52 and $97, respectively	83	153
Total other comprehensive income net of taxes	73	252
Comprehensive income	9,036	7,441
Unrealized holding gains on available-for-sale securities, income taxes	328	182
Accretion of unrealized loss on securities transferred to held-to-maturity, income taxes	6	139
Pension actuarial loss, income tax benefit	(340)	(259)
Amortization of pension actuarial losses recognized in salaries and benefits, income taxes	$ 52	$ 97