Loans - Additional Information (Detail)	3 Months Ended		12 Months Ended
	Mar. 31, 2020 USD ($) Contract Property	Mar. 31, 2019 USD ($) Contract	Dec. 31, 2019 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans serviced for others	$ 88,100,000		$ 95,700,000
Concentrations of loans related to a single industry	0		0
Loans classified as troubled debt restructurings	2,400,000		2,500,000
Reserves allocated to customers whose loan terms are modified in troubled debt restructurings	18,000		18,000
Loans payable in nonaccrual of interest status	$ 252,000
Number of loans restructured | Contract	1	1
Loans restructured, subsequently defaulted | Contract	0	1
Loans restructured, subsequently defaulted		$ 200,000
Number of properties acquired | Property	1
Other real estate real estate acquired through foreclosure	$ 99,000		99,000
Mortgage loans in process of foreclosure amount	44,000		50,000
Other repossessed assets	0		$ 0
Outstanding balance of commercial loans classified under credit risk, minimum amount	500,000
Loans listed as not rated under risk category, maximum amount	500,000
Performing [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans classified as troubled debt restructurings	$ 2,100,000