Allowance for Loan Losses - Additional Information (Detail)	3 Months Ended				12 Months Ended
	Sep. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Mar. 31, 2018 Contracts Contract	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan and Lease Losses, Write-offs					$ 454,000	$ 833,000	$ 390,000
Transfer Of Loans To Other Real Estate Owned	$ 2,225,000		$ 2,225,000			2,225,000
Residential Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Number of troubled debt restructurings | Contracts				1
Pre-modification outstanding recorded investment						2,675,000
Post-modification outstanding recorded investment					2,675,000
Allowance for Loan and Lease Losses, Write-offs						450,000
Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Number of troubled debt restructurings | Contract				1
Pre-modification outstanding recorded investment					17,000
Post-modification outstanding recorded investment						17,000
Commercial and Industrial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Post-modification outstanding recorded investment		$ 39,000
Allowance for Loan and Lease Losses, Write-offs					$ 137,000	$ 67,000