Condensed Financial Statements of Greene County Bancorp, Inc. - Condensed Statements of Financial Condition (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2012
ASSETS
Total assets	$ 674,161	$ 633,605
LIABILITIES AND SHAREHOLDERS' EQUITY [Abstract]
Total liabilities	612,961	577,497
Total shareholders' equity	61,200	56,108	52,664
Total liabilities and shareholders' equity	674,161	633,605
Parent Company [Member]
ASSETS
Cash and cash equivalents	2,817	2,114	4,247
Investment in subsidiaries	58,419	54,038
Prepaid expenses and other assets	16	16
Total assets	61,252	56,168
LIABILITIES AND SHAREHOLDERS' EQUITY [Abstract]
Total liabilities	52	60
Total shareholders' equity	61,200	56,108
Total liabilities and shareholders' equity	$ 61,252	$ 56,168