Loans, Leases and Other Real Estate - Additional Information (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Jun. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Mar. 31, 2017	Jul. 01, 2016	Jan. 07, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Troubled debt restructurings included in non accrual loans			$ 3,900,000		$ 2,700,000
Unfunded lending reserve			2,500,000		2,500,000
Other real estate owned			2,800,000		843,000
Other repossessed assets owned			0
Residential Property
Accounts, Notes, Loans and Financing Receivable [Line Items]
Other real estate owned			2,100,000		843,000
Impaired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest income on credit impaired loans			450,000	$ 515,000
Interest accrued on impaired loans			842,000	$ 1,200,000
Pascack Bancorp, Inc.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and debt securities acquired with deteriorated credit quality			170,000
Certain loans acquired in transfer not accounted for as debt securities, carrying amount, decrease since acquisition								$ 647,000
Total purchased credit impaired loans, experienced further credit deterioration and fully charged off						$ 127,000
Remaining loan amount paid	$ 218,000
Harmony Bank
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and debt securities acquired with deteriorated credit quality			503,000
Certain loans acquired in transfer not accounted for as debt securities, carrying amount, decrease since acquisition							$ 266,000
Remaining loan amount paid		$ 247,000
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		1,100,000,000
Home equity and consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Overdraft balances included in home equity and consumer loans			310,000		966,000
Residential Mortgages And Consumer Home Equity Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage loans that were in process of foreclosure			1,600,000		$ 2,700,000
Minimum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Group of impaired loans with recorded investment			$ 500,000