Loans Receivable - Impairment Status of Loans Receivable (Detail) - USD ($) $ in Thousands		Dec. 31, 2020	Jun. 30, 2020
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-impaired loans		$ 4,737,847	$ 4,494,981
Impaired loans with no allowance for impairment			43,316
Recorded investment			1,806
Allowance for impairment			(89)
Balance of impaired loans net of allowance for impairment			1,717
Total impaired loans, excluding allowance for impairment:			45,122
Unpaid principal balance of impaired loans			53,151
Loans and Leases Receivable, Gross		4,867,358	4,540,103
Unpaid principal balance of impaired loans:			45,122
Home Equity Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-impaired loans		64,713	81,363
Impaired loans with no allowance for impairment			1,557
Total impaired loans, excluding allowance for impairment:			1,557
Unpaid principal balance of impaired loans			1,950
Loans and Leases Receivable, Gross		65,298	82,920
Unpaid principal balance of impaired loans:			1,557
Multi-Family Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-impaired loans		2,054,427	2,056,606
Impaired loans with no allowance for impairment			2,962
Total impaired loans, excluding allowance for impairment:			2,962
Unpaid principal balance of impaired loans			3,544
Loans and Leases Receivable, Gross		2,076,483	2,059,568
Unpaid principal balance of impaired loans:			2,962
Non-Residential Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-impaired loans		1,052,820	936,805
Impaired loans with no allowance for impairment			22,516
Recorded investment			1,532
Allowance for impairment			(41)
Balance of impaired loans net of allowance for impairment			1,491
Total impaired loans, excluding allowance for impairment:			24,048
Unpaid principal balance of impaired loans			25,898
Loans and Leases Receivable, Gross		1,123,695	960,853
Unpaid principal balance of impaired loans:			24,048
Commercial Business [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-impaired loans		197,402	132,999
Impaired loans with no allowance for impairment			5,622
Recorded investment			167
Allowance for impairment			(47)
Balance of impaired loans net of allowance for impairment			120
Total impaired loans, excluding allowance for impairment:			5,789
Unpaid principal balance of impaired loans			8,778
Loans and Leases Receivable, Gross	[1]	202,010	138,788
Unpaid principal balance of impaired loans:			5,789
Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-impaired loans		76,391	20,961
Unpaid principal balance of impaired loans			73
Loans and Leases Receivable, Gross		90,398	20,961
Residential Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-impaired loans		1,287,976	1,262,256
Impaired loans with no allowance for impairment			10,659
Recorded investment			107
Allowance for impairment			(1)
Balance of impaired loans net of allowance for impairment			106
Total impaired loans, excluding allowance for impairment:			10,766
Unpaid principal balance of impaired loans			12,908
Loans and Leases Receivable, Gross		1,305,351	1,273,022
Unpaid principal balance of impaired loans:			10,766
Other Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-impaired loans		4,118	3,991
Loans and Leases Receivable, Gross		$ 4,123	$ 3,991

[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.