Loans - Schedule of Portfolio of Loans (Detail) - USD ($) $ in Thousands	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016
Financing Receivable Allowance For Credit Losses [Line Items]
Total loans	$ 2,114,932		$ 2,016,141
Allowance for loan losses	21,405	$ 21,610	21,202	$ 19,660	$ 18,970	$ 19,087
Deferred loan costs, net	(6,254)		(4,938)
Total	15,151		16,264
Loans, net	2,099,781		1,999,877
Commercial Loans [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total loans	900,817		822,616
Allowance for loan losses	12,808	13,095	12,542	10,821	10,182	10,824
Commercial Loans [Member] | Multifamily [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total loans	141,004		120,480
Commercial Loans [Member] | Nonresidential [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total loans	396,624		381,611
Commercial Loans [Member] | Land [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total loans	16,887		15,162
Commercial Loans [Member] | Construction [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total loans	127,691		116,863
Commercial Loans [Member] | Secured [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total loans	212,173		177,994
Commercial Loans [Member] | Unsecured [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total loans	6,438		10,506
Residential Mortgage Loans [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total loans	929,206		920,031
Allowance for loan losses	5,867	5,701	5,860	5,968	5,912	5,538
Residential Mortgage Loans [Member] | Construction [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total loans	40,623		49,092
Residential Mortgage Loans [Member] | One-to Four-Family [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total loans	888,583		870,939
Consumer Loans [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total loans	284,909		273,494
Allowance for loan losses	2,730	$ 2,814	2,800	$ 2,871	$ 2,876	$ 2,725
Consumer Loans [Member] | Home Equity [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total loans	187,771		195,852
Consumer Loans [Member] | Auto [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total loans	83,829		64,364
Consumer Loans [Member] | Marine [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total loans	1,404		1,526
Consumer Loans [Member] | Recreational Vehicle [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total loans	4,879		5,696
Consumer Loans [Member] | Other [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total loans	$ 7,026		$ 6,056