Loan Quality and Allowance for Loan Losses - Impairment Status of Loans Receivable (Detail) - USD ($) $ in Thousands	12 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2017
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-impaired loans	$ 4,706,368	$ 4,544,634
Impaired loans with no allowance for impairment	24,222	22,279
Recorded investment	363	1,002
Allowance for impairment	(31)	(306)
Balance of impaired loans net of allowance for impairment	332	696
Total impaired loans, excluding allowance for impairment:	24,585	23,281
Loans and Leases Receivable, Gross	4,730,953	4,567,915
Unpaid principal balance of impaired loans	31,948	37,705
Average balance of impaired loans	24,975	20,548	$ 24,597
Interest earned on impaired loans	230	212	165
Residential Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-impaired loans	1,331,415	1,285,423
Impaired loans with no allowance for impairment	12,266	11,255
Recorded investment	363	775
Allowance for impairment	(31)	(79)
Balance of impaired loans net of allowance for impairment	332	696
Total impaired loans, excluding allowance for impairment:	12,629	12,030
Loans and Leases Receivable, Gross	1,344,044	1,297,453
Unpaid principal balance of impaired loans	14,985	16,263
Average balance of impaired loans	12,883	9,465	12,536
Interest earned on impaired loans	129	131	107
Non-Residential Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-impaired loans	1,249,969	1,297,617
Impaired loans with no allowance for impairment	8,900	5,344
Total impaired loans, excluding allowance for impairment:	8,900	5,344
Loans and Leases Receivable, Gross	1,258,869	1,302,961
Unpaid principal balance of impaired loans	10,200	10,033
Average balance of impaired loans	8,242	6,484	6,242
Interest earned on impaired loans		5
Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-impaired loans	13,907	23,271
Loans and Leases Receivable, Gross	13,907	23,271
Unpaid principal balance of impaired loans	73	106
Average balance of impaired loans		106	448
Interest earned on impaired loans			7
Commercial Business [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-impaired loans	64,308	81,635
Impaired loans with no allowance for impairment	1,455	3,963
Recorded investment		227
Allowance for impairment		(227)
Total impaired loans, excluding allowance for impairment:	1,455	4,190
Loans and Leases Receivable, Gross	65,763	85,825
Unpaid principal balance of impaired loans	3,987	7,671
Average balance of impaired loans	2,212	2,690	3,114
Interest earned on impaired loans	67	44	15
Other Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-impaired loans	5,814	9,060
Loans and Leases Receivable, Gross	5,814	9,060
Multi-Family Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-impaired loans	1,946,321	1,758,468
Impaired loans with no allowance for impairment	70	116
Total impaired loans, excluding allowance for impairment:	70	116
Loans and Leases Receivable, Gross	1,946,391	1,758,584
Unpaid principal balance of impaired loans	779	930
Average balance of impaired loans	91	136	182
Home Equity Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-impaired loans	94,634	89,160
Impaired loans with no allowance for impairment	1,531	1,601
Total impaired loans, excluding allowance for impairment:	1,531	1,601
Loans and Leases Receivable, Gross	96,165	90,761
Unpaid principal balance of impaired loans	1,924	2,702
Average balance of impaired loans	1,547	1,667	2,075
Interest earned on impaired loans	$ 34	$ 32	$ 36