Loan Quality and Allowance for Loan Losses - Contractual Payment Status of Loans Receivable (Detail) - USD ($) $ in Thousands	Jun. 30, 2019	Jun. 30, 2018
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	$ 4,722,752	$ 4,557,210
Total past due	8,201	10,705
Loans and Leases Receivable, Gross	4,730,953	4,567,915
Residential Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	1,338,347	1,290,428
Total past due	5,697	7,025
Loans and Leases Receivable, Gross	1,344,044	1,297,453
Non-Residential Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	1,256,892	1,300,570
Total past due	1,977	2,391
Loans and Leases Receivable, Gross	1,258,869	1,302,961
Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	13,907	23,271
Loans and Leases Receivable, Gross	13,907	23,271
Commercial Business [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	65,668	85,065
Total past due	95	760
Loans and Leases Receivable, Gross	65,763	85,825
Other Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	5,754	8,917
Total past due	60	143
Loans and Leases Receivable, Gross	5,814	9,060
Multi-Family Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	1,946,391	1,758,584
Loans and Leases Receivable, Gross	1,946,391	1,758,584
Past due: 30-59 days [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	1,997	2,847
Past due: 30-59 days [Member] | Residential Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	1,680	1,457
Past due: 30-59 days [Member] | Non-Residential Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due		1,015
Past due: 30-59 days [Member] | Commercial Business [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	95	247
Past due: 30-59 days [Member] | Other Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	25	24
Past due: 60-89 days [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	522	578
Past due: 60-89 days [Member] | Residential Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	473	475
Past due: 60-89 days [Member] | Other Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	13	59
Past due: 90 days and over [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	5,682	7,280
Past due: 90 days and over [Member] | Residential Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	3,544	5,093
Past due: 90 days and over [Member] | Non-Residential Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	1,977	1,376
Past due: 90 days and over [Member] | Commercial Business [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due		513
Past due: 90 days and over [Member] | Other Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	22	60
Home Equity Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	95,793	90,375
Total past due	372	386
Loans and Leases Receivable, Gross	96,165	90,761
Home Equity Loans [Member] | Past due: 30-59 days [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	197	104
Home Equity Loans [Member] | Past due: 60-89 days [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	36	44
Home Equity Loans [Member] | Past due: 90 days and over [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	$ 139	$ 238