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, 2018	Dec. 31, 2017	Dec. 31, 2016	Mar. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Troubled debt restructurings included in non accrual loans				$ 3,600,000	$ 2,700,000
Unfunded lending reserve				2,300,000	2,500,000
Loans to these related parties				53,100,000	27,500,000
Loans to these related parties, additions				18,700,000
Repayment of loan from related parties				10,800,000
Mortgages held for sale				1,113,000	456,000
Residential real estate acquired through disclosure				830,000	800,000
Other repossessed assets owned				0	0
Writedown of other repossessed assets				70,000	98,000	$ 0
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				1,200,000,000	1,100,000,000
Residential Property
Accounts, Notes, Loans and Financing Receivable [Line Items]
Residential real estate acquired through disclosure				702,000	843,000
Pascack Bancorp, Inc.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and debt securities acquired with deteriorated credit quality				157,000			$ 127,000
Loans and debt securities acquired with deteriorated credit quality decrease		$ 661,000
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				495,000
Loans and debt securities acquired with deteriorated credit quality decrease	$ 274,000
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				1,100,000	1,500,000	$ 1,700,000
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				452,000	$ 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				1,500,000
Related Party Relationships, Commenced Or Ceased During 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans to these related parties, additions				$ 17,700,000