Subsequent events (Details)			12 Months Ended
	Jul. 22, 2019 Branch	Jul. 17, 2019 $ / shares	Jun. 30, 2019 $ / shares	Jun. 30, 2018 $ / shares
Dividends [Abstract]
Common stock, dividends declared (in dollars per share)			$ 0.40	$ 0.39
2018 Annual Dividend [Member]
Dividends [Abstract]
Common stock, dividends declared (in dollars per share)			$ 0.40
Subsequent Event [Member] | The Bank of Greene County [Member]
Business Operations [Abstract]
Number of Full Service Branches | Branch	16
Subsequent Event [Member] | 2019 Q4 Dividend [Member]
Dividends [Abstract]
Common stock, dividends declared (in dollars per share)		$ 0.11
Percentage of increase in cash dividend rate		10.00%
Dividends payable, date of record		Aug. 15, 2019
Dividends payable, date paid		Aug. 30, 2019
Dividends payable, date declared		Jul. 17, 2019
Subsequent Event [Member] | 2019 Annual Dividend [Member]
Dividends [Abstract]
Common stock, dividends declared (in dollars per share)		$ 0.44