Loans - Schedule of Portfolio of Loans (Detail) - USD ($) $ in Thousands	Sep. 30, 2016	Jun. 30, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Dec. 31, 2014
Financing Receivable Allowance For Credit Losses [Line Items]
Total loans	$ 1,489,802		$ 1,332,593
Allowance for loan losses	18,234	$ 17,172	17,712	$ 17,482	$ 16,881	$ 17,687
Deferred loan costs, net	(2,381)		(1,311)
Total	15,853		16,401
Loans, net	1,473,949		1,316,192
Commercial Loans [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total loans	494,183		369,752
Allowance for loan losses	9,794	8,958	8,077	7,701	6,389	5,690
Commercial Loans [Member] | Multifamily [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total loans	107,066		80,170
Commercial Loans [Member] | Nonresidential [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total loans	225,699		175,456
Commercial Loans [Member] | Land [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total loans	9,401		9,301
Commercial Loans [Member] | Construction [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total loans	45,137		38,812
Commercial Loans [Member] | Secured [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total loans	96,331		63,182
Commercial Loans [Member] | Unsecured [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total loans	10,549		2,831
Residential Mortgage Loans [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total loans	791,768		774,583
Allowance for loan losses	5,766	5,644	6,630	6,717	7,082	8,517
Residential Mortgage Loans [Member] | Construction [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total loans	35,875		40,898
Residential Mortgage Loans [Member] | One-to Four-Family [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total loans	755,893		733,685
Consumer Loans [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total loans	203,851		188,258
Allowance for loan losses	2,674	$ 2,570	3,005	$ 3,064	$ 3,410	$ 3,480
Consumer Loans [Member] | Home Equity [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total loans	162,979		161,338
Consumer Loans [Member] | Auto [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total loans	28,269		11,348
Consumer Loans [Member] | Marine [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total loans	1,859		2,699
Consumer Loans [Member] | Recreational Vehicle [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total loans	8,199		10,656
Consumer Loans [Member] | Other [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total loans	$ 2,545		$ 2,217