Fair Value - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Provision for credit losses	$ 38,395		$ 6,966
Other real estate owned property write-downs	161	$ 60
Valuation allowance for loan servicing rights with impairments	1,407	31	15	$ 29
Recoveries on loan servicing rights	$ 1,376	16	(14)
Net carrying amount other real estate owned and other repossessed property		43
Past due period of mortgage loans held for sale, days	90 days
Interest income for residential loans held for sale	$ 2,000	1,400	$ 500
States and political subdivisions
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3		4,000
Transfers into Level 3		4,100
Impaired Commercial and Commercial Real Estate Loans
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Principal amount of impaired commercial and commercial real estate loans	57,200	30,900
Valuation allowance	5,800	8,900
Provision for credit losses	$ 2,100	$ 4,100