Loan Quality and Allowance for Loan Losses - Credit-Rating Classification of Loans Receivable (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Jun. 30, 2018
Financing Receivable Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	$ 4,812,575	$ 4,567,915
Residential Mortgage [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	1,334,284	1,297,453
Non-Residential Mortgage [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	1,302,583	1,302,961
Construction [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	28,405	23,271
Commercial Business [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	70,059	85,825
Other Consumer [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	6,834	9,060
Multi-Family Mortgage [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	1,974,409	1,758,584
Non-Classified [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	4,774,836	4,538,570
Non-Classified [Member] | Residential Mortgage [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	1,319,107	1,283,040
Non-Classified [Member] | Non-Residential Mortgage [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	1,288,964	1,295,076
Non-Classified [Member] | Construction [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	28,405	23,271
Non-Classified [Member] | Commercial Business [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	64,254	80,947
Non-Classified [Member] | Other Consumer [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	6,765	8,937
Non-Classified [Member] | Multi-Family Mortgage [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	1,973,190	1,758,468
Special Mention [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	5,627	592
Special Mention [Member] | Residential Mortgage [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	486	493
Special Mention [Member] | Non-Residential Mortgage [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	1,130
Special Mention [Member] | Commercial Business [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	2,818	13
Special Mention [Member] | Other Consumer [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	34	61
Special Mention [Member] | Multi-Family Mortgage [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	1,130
Substandard [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	32,027	28,752
Substandard [Member] | Residential Mortgage [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	14,691	13,920
Substandard [Member] | Non-Residential Mortgage [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	12,489	7,885
Substandard [Member] | Commercial Business [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	2,903	4,865
Substandard [Member] | Other Consumer [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	34	61
Substandard [Member] | Multi-Family Mortgage [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	89	116
Doubtful [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	85	1
Doubtful [Member] | Commercial Business [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	84
Doubtful [Member] | Other Consumer [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	1	1
Total Classified Loans [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	37,739	29,345
Total Classified Loans [Member] | Residential Mortgage [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	15,177	14,413
Total Classified Loans [Member] | Non-Residential Mortgage [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	13,619	7,885
Total Classified Loans [Member] | Commercial Business [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	5,805	4,878
Total Classified Loans [Member] | Other Consumer [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	69	123
Total Classified Loans [Member] | Multi-Family Mortgage [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	1,219	116
Home Equity Loans [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	96,001	90,761
Home Equity Loans [Member] | Non-Classified [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	94,151	88,831
Home Equity Loans [Member] | Special Mention [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	29	25
Home Equity Loans [Member] | Substandard [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	1,821	1,905
Home Equity Loans [Member] | Total Classified Loans [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and Leases Receivable, Gross	$ 1,850	$ 1,930