Fair Value - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019	Dec. 31, 2018
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Provision expense for (recoveries from) credit losses	$ 22,545	$ 1,003	$ 39,495	$ 2,046
Net carrying amount other real estate owned and other repossessed property	47		47			$ 43
Other real estate owned property write-downs	87		98
Valuation allowance for loan servicing rights with impairments	2,253	32	2,253	32	$ 1,443	31	$ 17	$ 15
Valuation allowance for loan servicing rights with impairments, impairments during period	810	15	$ 2,222	17
Past due period of mortgage loans held for sale, days			90 days
Interest income for residential loans held for sale	500	300	$ 900	500
States and political subdivisions
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Transfers out of Level 3				4,000
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	44,300		44,300			30,900
Valuation allowance	8,800		8,800			$ 8,900
Provision expense for (recoveries from) credit losses	$ (300)	$ 1,100	$ 6,500	$ 2,300