Loans Receivable - Contractual Payment Status of Loans Receivable (Detail) - USD ($) $ in Thousands		Dec. 31, 2020	Jun. 30, 2020
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and Leases Receivable, Gross		$ 4,867,358	$ 4,540,103
Home Equity Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and Leases Receivable, Gross		65,298	82,920
Commercial Business [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and Leases Receivable, Gross	[1]	202,010	138,788
Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and Leases Receivable, Gross		90,398	20,961
Residential Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and Leases Receivable, Gross		1,305,351	1,273,022
Other Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and Leases Receivable, Gross		4,123	3,991
Non-Residential Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and Leases Receivable, Gross		1,123,695	960,853
Multi-Family Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and Leases Receivable, Gross		2,076,483	2,059,568
Past Due Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current		4,802,272	4,511,288
Total past due		65,086	28,815
Loans and Leases Receivable, Gross		4,867,358	4,540,103
Past Due Loans [Member] | Home Equity Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current		65,182	82,358
Total past due		116	562
Loans and Leases Receivable, Gross		65,298	82,920
Past Due Loans [Member] | Commercial Business [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current		201,527	138,439
Total past due		483	349
Loans and Leases Receivable, Gross		202,010	138,788
Past Due Loans [Member] | Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current		90,398	20,961
Loans and Leases Receivable, Gross		90,398	20,961
Past Due Loans [Member] | Residential Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current		1,297,164	1,264,267
Total past due		8,187	8,755
Loans and Leases Receivable, Gross		1,305,351	1,273,022
Past Due Loans [Member] | Other Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current		4,110	3,981
Total past due		13	10
Loans and Leases Receivable, Gross		4,123	3,991
Past Due Loans [Member] | Non-Residential Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current		1,083,879	941,714
Total past due		39,816	19,139
Loans and Leases Receivable, Gross		1,123,695	960,853
Past Due Loans [Member] | Past due: 30-59 days [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due		8,587	3,380
Past Due Loans [Member] | Past due: 30-59 days [Member] | Home Equity Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due			169
Past Due Loans [Member] | Past due: 30-59 days [Member] | Commercial Business [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due		183
Past Due Loans [Member] | Past due: 30-59 days [Member] | Residential Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due		2,718	3,211
Past Due Loans [Member] | Past due: 30-59 days [Member] | Other Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due		2
Past Due Loans [Member] | Past due: 30-59 days [Member] | Non-Residential Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due		2,713
Past Due Loans [Member] | Past due: 60-89 days [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due		18,080	15,534
Past Due Loans [Member] | Past due: 60-89 days [Member] | Home Equity Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due			13
Past Due Loans [Member] | Past due: 60-89 days [Member] | Residential Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due		271	1,038
Past Due Loans [Member] | Past due: 60-89 days [Member] | Other Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due		6	5
Past Due Loans [Member] | Past due: 60-89 days [Member] | Non-Residential Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due		14,529	14,478
Past Due Loans [Member] | Past due: 90 days and over [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due		38,419	9,901
Past Due Loans [Member] | Past due: 90 days and over [Member] | Home Equity Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due		116	380
Past Due Loans [Member] | Past due: 90 days and over [Member] | Commercial Business [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due		300	349
Past Due Loans [Member] | Past due: 90 days and over [Member] | Residential Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due		5,198	4,506
Past Due Loans [Member] | Past due: 90 days and over [Member] | Other Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due		5	5
Past Due Loans [Member] | Past due: 90 days and over [Member] | Non-Residential Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due		22,574	4,661
Past Due Loans [Member] | Multi-Family Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current		2,060,012	2,059,568
Total past due		16,471
Loans and Leases Receivable, Gross		2,076,483	$ 2,059,568
Past Due Loans [Member] | Multi-Family Mortgage [Member] | Past due: 30-59 days [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due		2,971
Past Due Loans [Member] | Multi-Family Mortgage [Member] | Past due: 60-89 days [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due		3,274
Past Due Loans [Member] | Multi-Family Mortgage [Member] | Past due: 90 days and over [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due		$ 10,226

[1] Includes Paycheck Protection Program (“PPP”) loans of $39.2 million and $69.0 million as of December 31, 2020 and June 30, 2020, respectively. The balance of PPP loans at December 31, 2020 includes loans acquired in conjunction with the Company’s acquisition of MSB on July 10, 2020.