Condensed Financial Statements of Greene County Bancorp, Inc., Condensed Statements of Financial Condition (Details) - USD ($) $ in Thousands	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2013
ASSETS [Abstract]
Total assets	$ 738,647	$ 674,161
LIABILITIES AND SHAREHOLDERS' EQUITY [Abstract]
Total liabilities	671,727	612,961
Total shareholders' equity	66,920	61,200	$ 56,108
Total liabilities and shareholders' equity	738,647	674,161
Parent Company [Member]
ASSETS [Abstract]
Cash and cash equivalents	544	2,817	$ 2,114
Investment in subsidiaries	66,412	58,419
Prepaid expenses and other assets	21	16
Total assets	66,977	61,252
LIABILITIES AND SHAREHOLDERS' EQUITY [Abstract]
Total liabilities	57	52
Total shareholders' equity	66,920	61,200
Total liabilities and shareholders' equity	$ 66,977	$ 61,252