Loan Quality and Allowance for Loan Losses - Contractual Payment Status of Loans Receivable (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Jun. 30, 2019
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	$ 4,627,157	$ 4,722,752
Total past due	26,563	8,201
Loans and Leases Receivable, Gross	4,653,720	4,730,953
Residential Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	1,313,195	1,338,347
Total past due	6,555	5,697
Loans and Leases Receivable, Gross	1,319,750	1,344,044
Non-Residential Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	1,214,524	1,256,892
Total past due	16,439	1,977
Loans and Leases Receivable, Gross	1,230,963	1,258,869
Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	14,501	13,907
Total past due	136
Loans and Leases Receivable, Gross	14,637	13,907
Commercial Business [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	66,749	65,668
Total past due	140	95
Loans and Leases Receivable, Gross	66,889	65,763
Other Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	5,160	5,754
Total past due	49	60
Loans and Leases Receivable, Gross	5,209	5,814
Multi-Family Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	1,919,907	1,946,391
Total past due	3,061
Loans and Leases Receivable, Gross	1,922,968	1,946,391
Past due: 30-59 days [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	20,312	1,997
Past due: 30-59 days [Member] \| Residential Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	2,721	1,680
Past due: 30-59 days [Member] \| Non-Residential Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	14,462
Past due: 30-59 days [Member] \| Commercial Business [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	49	95
Past due: 30-59 days [Member] \| Other Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	19	25
Past due: 30-59 days [Member] \| Multi-Family Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	3,061
Past due: 60-89 days [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	689	522
Past due: 60-89 days [Member] \| Residential Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	470	473
Past due: 60-89 days [Member] \| Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	136
Past due: 60-89 days [Member] \| Commercial Business [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	68
Past due: 60-89 days [Member] \| Other Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	15	13
Past due: 90 days and over [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	5,562	5,682
Past due: 90 days and over [Member] \| Residential Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	3,364	3,544
Past due: 90 days and over [Member] \| Non-Residential Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	1,977	1,977
Past due: 90 days and over [Member] \| Commercial Business [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	23
Past due: 90 days and over [Member] \| Other Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	15	22
Home Equity Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	93,121	95,793
Total past due	183	372
Loans and Leases Receivable, Gross	93,304	96,165
Home Equity Loans [Member] \| Past due: 30-59 days [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due		197
Home Equity Loans [Member] \| Past due: 60-89 days [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due		36
Home Equity Loans [Member] \| Past due: 90 days and over [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	$ 183	$ 139