Loans and Leases and Other Real Estate - Additional Information (Detail) - USD ($)			3 Months Ended	12 Months Ended
	Jul. 01, 2016	Jan. 07, 2016	Jun. 30, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Mar. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Troubled debt restructurings included in non accrual loans				$ 2,700,000	$ 2,400,000
Unfunded lending reserve				2,500,000	2,500,000
Loans to these related parties				27,500,000	22,300,000
Loans to these related parties, additions				9,700,000
Repayment of loan from related parties				4,500,000
Mortgages held for sale				456,000	1,742,000
Other real estate owned				843,000	1,100,000
Other repossessed assets owned				0	9,000
Writedown of other repossessed assets				98,000	0	$ 119,000
Federal Home Loan Bank of New York
Accounts, Notes, Loans and Financing Receivable [Line Items]
Residential loans pledged for potential borrowings at the Federal Home Loan Bank of New York				1,100,000,000	942,000,000
Residential Property
Accounts, Notes, Loans and Financing Receivable [Line Items]
Other real estate owned				843,000	1,100,000
Pascack Bancorp, Inc.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and debt securities acquired with deteriorated credit quality				190,000			$ 127,000
Loans and debt securities acquired with deteriorated credit quality decrease		$ 627,000
Certain Loans Acquired In Transfer Not Accounted For As Debt Securities Payments			$ 218,000
Harmony Bank
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and debt securities acquired with deteriorated credit quality				520,000
Loans and debt securities acquired with deteriorated credit quality decrease	$ 249,000
Certain Loans Acquired In Transfer Not Accounted For As Debt Securities Payments			$ 247,000
Impaired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest accrued on impaired loans and leases				1,500,000	1,700,000	$ 1,600,000
Minimum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Group of impaired loans with recorded investment				500,000
Home equity and consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Overdraft balances included in home equity and consumer loans				966,000	$ 364,000
Residential Mortgages And Consumer Home Equity Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage loans that were in process of foreclosure				$ 2,700,000