Fair Value - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Net carrying amount other real estate owned and other repossessed property	$ 43	$ 68
Other real estate owned property write-downs	60	600
Valuation allowance for loan servicing rights with impairments	31	15	$ 29	$ 68
Recoveries on loan servicing rights	$ 16	(14)	(39)
Past due period of mortgage loans held for sale, days	90 days
Interest income for residential loans held for sale	$ 1,400	500	$ 200
States and Political Subdivisions [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Transfers out of Level 3	4,000
Transfers into Level 3		4,100
Impaired Commercial and Commercial Real Estate Loans [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Principal amount of impaired commercial and commercial real estate loans	30,900	49,300
Valuation allowance	8,900	12,900
Provision for loan losses expensed	$ 4,100	$ 9,900