Securities, Debt Securities Available for Sale (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2019	Mar. 31, 2018	Jun. 30, 2018
Comparative summary of debt securities available for sale [Abstract]
Amortized cost	$ 35,670		$ 35,670		$ 44,250
Gross unrealized gains	35		35		64
Gross unrealized losses	692		692		1,188
Fair value	35,013		35,013		43,126
Proceeds from sales of debt securities available for sale			0	$ 29,505
Cash Flow Hedging [Member] \| Interest Rate Swaps [Member]
Comparative summary of debt securities available for sale [Abstract]
Fair value of debt securities available for sale pledged as collateral	0		0		0
Advances [Member]
Comparative summary of debt securities available for sale [Abstract]
Fair value of debt securities available for sale pledged as collateral	13,485		13,485		15,507
Municipal Deposits [Member]
Comparative summary of debt securities available for sale [Abstract]
Fair value of debt securities available for sale pledged as collateral	0		0		0
Available-for-sale Securities [Member]
Comparative summary of debt securities available for sale [Abstract]
Proceeds from sales of debt securities available for sale	0	$ 0	0	29,505
Debt securities available for sale sold, amortized cost				29,830
Debt securities available for sale, gross realized losses				324
Other-than-temporary impairment charges on debt securities available for sale	0	$ 0	$ 0	$ 0
Mortgage Backed Securities [Member] \| Minimum [Member]
Comparative summary of debt securities available for sale [Abstract]
Contractual maturities of mortgage-backed debt securities available for sale			20 years
Residential MBS [Member]
Comparative summary of debt securities available for sale [Abstract]
Amortized cost	19		$ 19		70
Gross unrealized gains	1		1		1
Gross unrealized losses	0		0		0
Fair value	20		20		71
Commercial MBS [Member]
Comparative summary of debt securities available for sale [Abstract]
Amortized cost	3,959		3,959		4,074
Gross unrealized gains	34		34		63
Gross unrealized losses	0		0		0
Fair value	3,993		3,993		4,137
CMO [Member]
Comparative summary of debt securities available for sale [Abstract]
Amortized cost	31,692		31,692		40,106
Gross unrealized gains	0		0		0
Gross unrealized losses	692		692		1,188
Fair value	$ 31,000		$ 31,000		$ 38,918

Oritani Financial Corp 10-Q