Loan Quality and Allowance for Loan Losses - Contractual Payment Status of Loans Receivable (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Jun. 30, 2018
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	$ 4,794,927	$ 4,557,210
Total past due	17,648	10,705
Loans and Leases Receivable, Gross	4,812,575	4,567,915
Residential Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	1,324,533	1,290,428
Total past due	9,751	7,025
Loans and Leases Receivable, Gross	1,334,284	1,297,453
Non-Residential Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	1,295,530	1,300,570
Total past due	7,053	2,391
Loans and Leases Receivable, Gross	1,302,583	1,302,961
Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	28,405	23,271
Loans and Leases Receivable, Gross	28,405	23,271
Commercial Business [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	69,564	85,065
Total past due	495	760
Loans and Leases Receivable, Gross	70,059	85,825
Other Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	6,748	8,917
Total past due	86	143
Loans and Leases Receivable, Gross	6,834	9,060
Multi-Family Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	1,974,409	1,758,584
Loans and Leases Receivable, Gross	1,974,409	1,758,584
Past due: 30-59 days [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	7,702	2,847
Past due: 30-59 days [Member] | Residential Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	2,428	1,457
Past due: 30-59 days [Member] | Non-Residential Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	5,076	1,015
Past due: 30-59 days [Member] | Commercial Business [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	169	247
Past due: 30-59 days [Member] | Other Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	21	24
Past due: 60-89 days [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	1,775	578
Past due: 60-89 days [Member] | Residential Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	1,664	475
Past due: 60-89 days [Member] | Commercial Business [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	50
Past due: 60-89 days [Member] | Other Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	33	59
Past due: 90+ days [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	8,171	7,280
Past due: 90+ days [Member] | Residential Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	5,659	5,093
Past due: 90+ days [Member] | Non-Residential Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	1,977	1,376
Past due: 90+ days [Member] | Commercial Business [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	276	513
Past due: 90+ days [Member] | Other Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	32	60
Home Equity Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	95,738	90,375
Total past due	263	386
Loans and Leases Receivable, Gross	96,001	90,761
Home Equity Loans [Member] | Past due: 30-59 days [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	8	104
Home Equity Loans [Member] | Past due: 60-89 days [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	28	44
Home Equity Loans [Member] | Past due: 90+ days [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	$ 227	$ 238