Loan Quality and Allowance for Loan Losses - Performance Status of Loans Receivable (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Jun. 30, 2019
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and Leases Receivable, Gross	$ 4,653,720	$ 4,730,953
Residential Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and Leases Receivable, Gross	1,319,750	1,344,044
Non-Residential Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and Leases Receivable, Gross	1,230,963	1,258,869
Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and Leases Receivable, Gross	14,637	13,907
Commercial Business [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and Leases Receivable, Gross	66,889	65,763
Other Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and Leases Receivable, Gross	5,209	5,814
Multi-Family Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and Leases Receivable, Gross	1,922,968	1,946,391
Home Equity Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and Leases Receivable, Gross	93,304	96,165
Performing Financing Receivable [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and Leases Receivable, Gross	4,631,939	4,710,683
Performing Financing Receivable [Member] \| Residential Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and Leases Receivable, Gross	1,311,214	1,334,101
Performing Financing Receivable [Member] \| Non-Residential Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and Leases Receivable, Gross	1,222,213	1,249,969
Performing Financing Receivable [Member] \| Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and Leases Receivable, Gross	14,637	13,907
Performing Financing Receivable [Member] \| Commercial Business [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and Leases Receivable, Gross	66,327	65,294
Performing Financing Receivable [Member] \| Other Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and Leases Receivable, Gross	5,194	5,792
Performing Financing Receivable [Member] \| Multi-Family Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and Leases Receivable, Gross	1,919,907	1,946,321
Performing Financing Receivable [Member] \| Home Equity Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and Leases Receivable, Gross	92,447	95,299
Nonperforming Financing Receivable [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
90 days and over past due accruing	15	22
Nonaccrual	21,766	20,248
Total nonperforming	21,781	20,270
Nonperforming Financing Receivable [Member] \| Residential Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual	8,536	9,943
Total nonperforming	8,536	9,943
Nonperforming Financing Receivable [Member] \| Non-Residential Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual	8,750	8,900
Total nonperforming	8,750	8,900
Nonperforming Financing Receivable [Member] \| Commercial Business [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual	562	469
Total nonperforming	562	469
Nonperforming Financing Receivable [Member] \| Other Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
90 days and over past due accruing	15	22
Total nonperforming	15	22
Nonperforming Financing Receivable [Member] \| Multi-Family Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual	3,061	70
Total nonperforming	3,061	70
Nonperforming Financing Receivable [Member] \| Home Equity Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual	857	866
Total nonperforming	$ 857	$ 866

Amount of financing receivable 90 days or more past due and still accruing.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 16
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=119407570&loc=SL82919258-210447

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 7
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=118936363&loc=d3e5111-111524

Reference 3: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 55
-Paragraph 80
-URI http://asc.fasb.org/extlink&oid=118955255&loc=SL82922355-210448

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Amount of financing receivable on nonaccrual status.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
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-Topic 310
-SubTopic 10
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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-Topic 326
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-Paragraph 16
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Amount before allowance of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Includes deferred interest and fees, undisbursed portion of loan balance, unamortized costs and premiums and discounts from face amounts. Excludes loans and leases covered under loss sharing agreements.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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-Topic 310
-SubTopic 10
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