Loans - Schedule of Portfolio of Loans (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Financing Receivable Allowance For Credit Losses [Line Items]
Total loans	$ 2,016,141	$ 1,519,477
Allowance for loan losses	21,202	19,087	$ 17,712	$ 17,687
Deferred loan fees, net	(4,938)	(3,187)
Total	16,264	15,900
Loans, net	1,999,877	1,503,577
Commercial Loans [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total loans	822,616	504,258
Allowance for loan losses	12,542	10,824	8,077	5,690
Commercial Loans [Member] | Multifamily [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total loans	120,480	93,597
Commercial Loans [Member] | Nonresidential [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total loans	381,611	231,401
Commercial Loans [Member] | Land [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total loans	15,162	8,373
Commercial Loans [Member] | Construction [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total loans	116,863	68,158
Commercial Loans [Member] | Secured [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total loans	177,994	95,343
Commercial Loans [Member] | Unsecured [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total loans	10,506	7,386
Residential Mortgage Loans [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total loans	920,031	798,621
Allowance for loan losses	5,860	5,538	6,630	8,517
Residential Mortgage Loans [Member] | Construction [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total loans	49,092	35,695
Residential Mortgage Loans [Member] | One-to Four-Family [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total loans	870,939	762,926
Consumer Loans [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total loans	273,494	216,598
Allowance for loan losses	2,800	2,725	$ 3,005	$ 3,480
Consumer Loans [Member] | Home Equity [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total loans	195,852	165,054
Consumer Loans [Member] | Auto [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total loans	64,364	39,609
Consumer Loans [Member] | Marine [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total loans	1,526	1,796
Consumer Loans [Member] | Recreational Vehicle [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total loans	5,696	7,602
Consumer Loans [Member] | Other [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total loans	$ 6,056	$ 2,537