Loans - Schedule of Portfolio of Loans (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Financing Receivable Allowance For Credit Losses [Line Items]
Total loans	$ 2,077,570	$ 2,016,141
Allowance for loan losses	21,610	21,202	$ 18,970	$ 19,087
Deferred loan costs, net	(5,483)	(4,938)
Total	16,127	16,264
Loans, net	2,061,443	1,999,877
Commercial Loans [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total loans	873,134	822,616
Allowance for loan losses	13,095	12,542	10,182	10,824
Commercial Loans [Member] | Multifamily [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total loans	137,836	120,480
Commercial Loans [Member] | Nonresidential [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total loans	384,533	381,611
Commercial Loans [Member] | Land [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total loans	15,452	15,162
Commercial Loans [Member] | Construction [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total loans	134,181	116,863
Commercial Loans [Member] | Secured [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total loans	194,756	177,994
Commercial Loans [Member] | Unsecured [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total loans	6,376	10,506
Residential Mortgage Loans [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total loans	925,326	920,031
Allowance for loan losses	5,701	5,860	5,912	5,538
Residential Mortgage Loans [Member] | Construction [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total loans	42,453	49,092
Residential Mortgage Loans [Member] | One-to Four-Family [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total loans	882,873	870,939
Consumer Loans [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total loans	279,110	273,494
Allowance for loan losses	2,814	2,800	$ 2,876	$ 2,725
Consumer Loans [Member] | Home Equity [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total loans	191,626	195,852
Consumer Loans [Member] | Auto [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total loans	74,054	64,364
Consumer Loans [Member] | Marine [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total loans	1,488	1,526
Consumer Loans [Member] | Recreational Vehicle [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total loans	5,241	5,696
Consumer Loans [Member] | Other [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total loans	$ 6,701	$ 6,056