Loans - Schedule of Portfolio of Loans (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Jun. 30, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Dec. 31, 2017
Financing Receivable Allowance For Credit Losses [Line Items]
Total loans	$ 2,261,223		$ 2,190,662
Allowance for loan losses	19,987	$ 20,482	20,443	$ 21,332	$ 21,405	$ 21,202
Deferred loan costs, net	(7,271)		(6,623)
Total	12,716		13,820
Loans, net	2,248,507		2,176,842
Commercial Loans [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total loans	994,047		942,931
Allowance for loan losses	12,089	12,547	11,875	12,582	12,808	12,542
Commercial Loans [Member] | Multifamily [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total loans	166,027		134,143
Commercial Loans [Member] | Nonresidential [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total loans	409,687		409,979
Commercial Loans [Member] | Land [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total loans	19,653		16,830
Commercial Loans [Member] | Construction [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total loans	127,388		141,686
Commercial Loans [Member] | Secured [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total loans	264,704		233,306
Commercial Loans [Member] | Unsecured [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total loans	6,588		6,987
Residential Mortgage Loans [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total loans	983,535		970,690
Allowance for loan losses	5,426	5,458	5,923	5,981	5,867	5,860
Residential Mortgage Loans [Member] | Construction [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total loans	44,636		43,435
Residential Mortgage Loans [Member] | One-to Four-Family [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total loans	938,899		927,255
Consumer Loans [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total loans	283,641		277,041
Allowance for loan losses	2,472	$ 2,477	2,645	$ 2,769	$ 2,730	$ 2,800
Consumer Loans [Member] | Home Equity [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total loans	183,622		185,661
Consumer Loans [Member] | Auto [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total loans	87,061		78,686
Consumer Loans [Member] | Marine [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total loans	1,065		1,206
Consumer Loans [Member] | Recreational Vehicle [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total loans	3,246		4,347
Consumer Loans [Member] | Other [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total loans	$ 8,647		$ 7,141