Fair Value Measurements - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Fair Value Measurements Disclosure [Line Items]
Percentage of securities using market-based information	100.00%
Transfer of equity security to non-marketable equity securities, included in other assets	$ 0	$ 0
Short-term borrowings approximate fair value for amounts that mature, days, less than	90 days
Fair value, measurements, nonrecurring
Fair Value Measurements Disclosure [Line Items]
Impaired loans, carrying amount	$ 44,900,000
Allocated allowance for loan losses	13,200,000	5,000,000
Provision for fair value measurements included in allowance for loan losses	36,000,000.0
Carrying amount of OREO	4,400,000
Written down of OREO	2,800,000
Loss from OREO included in earnings	1,600,000
Commercial loan | Minimum
Fair Value Measurements Disclosure [Line Items]
Financing receivable, individual reserves in default, threshold	1,000,000.0
Commercial and Consumer Loans | Maximum
Fair Value Measurements Disclosure [Line Items]
Financing receivable, individual reserves in default, threshold	1,000,000.0
Mortgage Servicing Rights
Fair Value Measurements Disclosure [Line Items]
Valuation allowance for impairment of recognized servicing assets, balance	7,300,000	1,500,000
Mortgage Servicing Rights | Fair value, measurements, nonrecurring
Fair Value Measurements Disclosure [Line Items]
Servicing asset	42,900,000
Valuation allowance for impairment of recognized servicing assets, balance	7,300,000
Servicing asset, carrying value	35,600,000
Mortgage Servicing Rights | Fair value, measurements, nonrecurring | Provision Expense
Fair Value Measurements Disclosure [Line Items]
Valuation allowance for impairment of recognized servicing assets, provision expense	5,800,000
SBA-Guaranteed Loan Servicing
Fair Value Measurements Disclosure [Line Items]
Valuation allowance for impairment of recognized servicing assets, balance	1,100,000	$ 1,200,000
SBA-Guaranteed Loan Servicing | Fair value, measurements, nonrecurring
Fair Value Measurements Disclosure [Line Items]
Servicing asset	4,000,000.0
Valuation allowance for impairment of recognized servicing assets, balance	1,100,000
Servicing asset, carrying value	2,900,000
Valuation allowance for impairment of recognized servicing assets, provision expense	$ 100,000