Loan Quality and Allowance for Loan Losses - Allowance for Loan Losses and Balance 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, Allowance for Credit Losses [Line Items]
Allowance	$ 32,731	$ 29,445	$ 30,865	$ 29,286
Allowance, Loans individually evaluated for impairment	352		352		$ 306
Allowance, Loans collectively evaluated for impairment	33,174		33,174		30,559
Allowance	33,526	30,066	33,526	30,066
Loans individually evaluated for impairment	25,563		25,563		22,913
Loans collectively evaluated for impairment	4,786,665		4,786,665		4,544,634
Loans and Leases Receivable, Gross	4,812,575		4,812,575		4,567,915
Loans receivable, unamortized yield adjustments	(59,183)		(59,183)		(66,567)
Loans receivable	4,753,392		4,753,392		4,501,348
Total charge offs	(199)	(406)	(461)	(1,014)
Total recoveries	23	91	51	228
Total provision (reversal) for Loan Losses	971	936	3,071	1,566
Residential Mortgage [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance	2,594	2,501	2,479	2,384
Allowance, Loans individually evaluated for impairment	41		41		79
Allowance, Loans collectively evaluated for impairment	2,936		2,936		2,400
Allowance	2,977	2,440	2,977	2,440
Loans individually evaluated for impairment	13,856		13,856		11,931
Loans collectively evaluated for impairment	1,320,338		1,320,338		1,285,423
Loans and Leases Receivable, Gross	1,334,284		1,334,284		1,297,453
Total charge offs	(1)	(143)	(83)	(410)
Total recoveries		57		77
Total provision (reversal) for Loan Losses	384	25	581	389
Non-Residential Mortgage [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance	9,945	9,893	9,787	9,939
Allowance, Loans collectively evaluated for impairment	9,918		9,918		9,787
Allowance	9,918	9,665	9,918	9,665
Loans individually evaluated for impairment	7,993		7,993		5,344
Loans collectively evaluated for impairment	1,294,590		1,294,590		1,297,617
Loans and Leases Receivable, Gross	1,302,583		1,302,583		1,302,961
Total charge offs			(54)	(38)
Total recoveries	1		2
Total provision (reversal) for Loan Losses	(28)	(228)	183	(236)
Construction [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance	293	89	258	35
Allowance, Loans collectively evaluated for impairment	305		305		258
Allowance	305	246	305	246
Loans collectively evaluated for impairment	28,405		28,405		23,271
Loans and Leases Receivable, Gross	28,405		28,405		23,271
Total charge offs
Total recoveries
Total provision (reversal) for Loan Losses	12	157	47	211
Commercial Business [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance	2,803	1,948	2,552	1,709
Allowance, Loans individually evaluated for impairment	311		311		227
Allowance, Loans collectively evaluated for impairment	2,203		2,203		2,325
Allowance	2,514	2,706	2,514	2,706
Loans individually evaluated for impairment	2,067		2,067		3,921
Loans collectively evaluated for impairment	67,735		67,735		81,635
Loans and Leases Receivable, Gross	70,059		70,059		85,825
Total charge offs	(166)		(185)	(6)
Total recoveries				34
Total provision (reversal) for Loan Losses	(123)	758	147	969
Other Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance	345	737	413	777
Allowance, Loans collectively evaluated for impairment	253		253		413
Allowance	253	643	253	643
Loans collectively evaluated for impairment	6,834		6,834		9,060
Loans and Leases Receivable, Gross	6,834		6,834		9,060
Total charge offs	(32)	(263)	(139)	(560)
Total recoveries	22	34	49	52
Total provision (reversal) for Loan Losses	(82)	135	(70)	374
Multi-Family Mortgage [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance	16,317	13,807	14,946	13,941
Allowance, Loans collectively evaluated for impairment	17,095		17,095		14,946
Allowance	17,095	13,909	17,095	13,909
Loans individually evaluated for impairment	89		89		116
Loans collectively evaluated for impairment	1,974,320		1,974,320		1,758,468
Loans and Leases Receivable, Gross	1,974,409		1,974,409		1,758,584
Total charge offs
Total recoveries
Total provision (reversal) for Loan Losses	778	102	2,149	(32)
Receivables Acquired with Deteriorated Credit Quality [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans acquired with deteriorated credit quality	347		347		368
Receivables Acquired with Deteriorated Credit Quality [Member] | Residential Mortgage [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans acquired with deteriorated credit quality	90		90		99
Receivables Acquired with Deteriorated Credit Quality [Member] | Commercial Business [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans acquired with deteriorated credit quality	257		257		269
Home Equity Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance	434	470	430	501
Allowance, Loans collectively evaluated for impairment	464		464		430
Allowance	464	457	464	457
Loans individually evaluated for impairment	1,558		1,558		1,601
Loans collectively evaluated for impairment	94,443		94,443		89,160
Loans and Leases Receivable, Gross	96,001		96,001		$ 90,761
Total charge offs
Total recoveries				65
Total provision (reversal) for Loan Losses	$ 30	$ (13)	$ 34	$ (109)