Loan Quality and Allowance for Loan Losses - Impairment Status of Loans Receivable (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Jun. 30, 2018
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-impaired loans	$ 4,786,665		$ 4,786,665		$ 4,544,634
Impaired loans with no allowance for impairment	25,183		25,183		22,279
Recorded investment	727		727		1,002
Allowance for impairment	(352)		(352)		(306)
Balance of impaired loans net of allowance for impairment	375		375		696
Total impaired loans, excluding allowance for impairment:	25,910		25,910		23,281
Loans and Leases Receivable, Gross	4,812,575		4,812,575		4,567,915
Unpaid principal balance of impaired loans	40,510		40,510		37,705
Average balance of impaired loans	25,684	$ 20,762	24,479	$ 21,121
Interest earned on impaired loans	68	41	111	87
Residential Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-impaired loans	1,320,338		1,320,338		1,285,423
Impaired loans with no allowance for impairment	13,531		13,531		11,255
Recorded investment	415		415		775
Allowance for impairment	(41)		(41)		(79)
Balance of impaired loans net of allowance for impairment	374		374		696
Total impaired loans, excluding allowance for impairment:	13,946		13,946		12,030
Loans and Leases Receivable, Gross	1,334,284		1,334,284		1,297,453
Unpaid principal balance of impaired loans	19,133		19,133		16,263
Average balance of impaired loans	13,228	8,860	12,718	9,441
Interest earned on impaired loans	33	31	65	66
Non-Residential Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-impaired loans	1,294,590		1,294,590		1,297,617
Impaired loans with no allowance for impairment	7,993		7,993		5,344
Total impaired loans, excluding allowance for impairment:	7,993		7,993		5,344
Loans and Leases Receivable, Gross	1,302,583		1,302,583		1,302,961
Unpaid principal balance of impaired loans	11,516		11,516		10,033
Average balance of impaired loans	8,146	7,254	7,626	6,755
Interest earned on impaired loans		2		4
Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-impaired loans	28,405		28,405		23,271
Loans and Leases Receivable, Gross	28,405		28,405		23,271
Unpaid principal balance of impaired loans	106		106		106
Average balance of impaired loans		63		196
Commercial Business [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-impaired loans	67,735		67,735		81,635
Impaired loans with no allowance for impairment	2,012		2,012		3,963
Recorded investment	312		312		227
Allowance for impairment	(311)		(311)		(227)
Balance of impaired loans net of allowance for impairment	1		1
Total impaired loans, excluding allowance for impairment:	2,324		2,324		4,190
Loans and Leases Receivable, Gross	70,059		70,059		85,825
Unpaid principal balance of impaired loans	6,067		6,067		7,671
Average balance of impaired loans	2,644	2,865	2,468	2,836
Interest earned on impaired loans	27	1	29	2
Other Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-impaired loans	6,834		6,834		9,060
Loans and Leases Receivable, Gross	6,834		6,834		9,060
Multi-Family Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-impaired loans	1,974,320		1,974,320		1,758,468
Impaired loans with no allowance for impairment	89		89		116
Total impaired loans, excluding allowance for impairment:	89		89		116
Loans and Leases Receivable, Gross	1,974,409		1,974,409		1,758,584
Unpaid principal balance of impaired loans	930		930		930
Average balance of impaired loans	95	141	101	146
Home Equity Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-impaired loans	94,443		94,443		89,160
Impaired loans with no allowance for impairment	1,558		1,558		1,601
Total impaired loans, excluding allowance for impairment:	1,558		1,558		1,601
Loans and Leases Receivable, Gross	96,001		96,001		90,761
Unpaid principal balance of impaired loans	2,758		2,758		$ 2,702
Average balance of impaired loans	1,571	1,579	1,566	1,747
Interest earned on impaired loans	$ 8	$ 7	$ 17	$ 15