Loans and Other Real Estate - Narrative (Detail) - USD ($)	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Jan. 04, 2019	Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and debt securities acquired with deteriorated credit quality	$ 12,205,000			$ 652,000
Troubled debt restructurings included in non accrual loans	1,600,000			3,600,000
Unfunded lending reserve	1,800,000			2,300,000
Other real estate owned	944,000			830,000
Other repossessed assets owned	0			0
Residential Property
Accounts, Notes, Loans and Financing Receivable [Line Items]
Other real estate owned	879,000			702,000
Impaired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest income on credit impaired loans	342,000	$ 450,000
Interest accrued on impaired loans	703,000	$ 842,000
Highlands Bancorp, Inc.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and debt securities acquired with deteriorated credit quality	11,627,000		$ 13,800,000	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	1,350,000,000			1,160,000,000
Home equity and consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Overdraft balances included in home equity and consumer loans	391,000			452,000
Residential Mortgages And Consumer Home Equity Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage loans that were in process of foreclosure	1,000,000.0			$ 1,500,000
Minimum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Group of impaired loans with recorded investment	$ 500,000