Loan Quality and Allowance for Loan Losses - Performance Status of Loans Receivable (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Jun. 30, 2018
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and Leases Receivable, Gross	$ 4,812,575	$ 4,567,915
Residential Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and Leases Receivable, Gross	1,334,284	1,297,453
Non-Residential Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and Leases Receivable, Gross	1,302,583	1,302,961
Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and Leases Receivable, Gross	28,405	23,271
Commercial Business [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and Leases Receivable, Gross	70,059	85,825
Other Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and Leases Receivable, Gross	6,834	9,060
Multi-Family Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and Leases Receivable, Gross	1,974,409	1,758,584
Home Equity Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and Leases Receivable, Gross	96,001	90,761
Performing Financing Receivable [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and Leases Receivable, Gross	4,791,800	4,551,056
Performing Financing Receivable [Member] | Residential Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and Leases Receivable, Gross	1,323,105	1,288,261
Performing Financing Receivable [Member] | Non-Residential Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and Leases Receivable, Gross	1,294,882	1,297,621
Performing Financing Receivable [Member] | Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and Leases Receivable, Gross	28,405	23,271
Performing Financing Receivable [Member] | Commercial Business [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and Leases Receivable, Gross	69,183	84,587
Performing Financing Receivable [Member] | Other Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and Leases Receivable, Gross	6,802	9,000
Performing Financing Receivable [Member] | Multi-Family Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and Leases Receivable, Gross	1,974,320	1,758,468
Performing Financing Receivable [Member] | Home Equity Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and Leases Receivable, Gross	95,103	89,848
Nonperforming Financing Receivable [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
90+ days past due accruing	32	60
Nonaccrual	20,743	16,799
Total nonperforming	20,775	16,859
Nonperforming Financing Receivable [Member] | Residential Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
90+ days past due accruing	0
Nonaccrual	11,179	9,192
Total nonperforming	11,179	9,192
Nonperforming Financing Receivable [Member] | Non-Residential Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
90+ days past due accruing	0
Nonaccrual	7,701	5,340
Total nonperforming	7,701	5,340
Nonperforming Financing Receivable [Member] | Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
90+ days past due accruing	0
Nonaccrual	0
Total nonperforming	0
Nonperforming Financing Receivable [Member] | Commercial Business [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
90+ days past due accruing	0
Nonaccrual	876	1,238
Total nonperforming	876	1,238
Nonperforming Financing Receivable [Member] | Other Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
90+ days past due accruing	32	60
Nonaccrual	0
Total nonperforming	32	60
Nonperforming Financing Receivable [Member] | Multi-Family Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
90+ days past due accruing	0
Nonaccrual	89	116
Total nonperforming	89	116
Nonperforming Financing Receivable [Member] | Home Equity Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
90+ days past due accruing	0
Nonaccrual	898	913
Total nonperforming	$ 898	$ 913