Fair Value Measurement - Quantitative Information about Recurring Fair Value Measurements (Detail) - Mortgage servicing rights $ in Thousands	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	$ 5,092	$ 6,200	$ 7,098	$ 6,687
Minimum | Constant prepayment rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Constant prepayment rate	0.144	0.050
Minimum | Discount rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Constant prepayment rate	0.100	0.120
Maximum | Constant prepayment rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Constant prepayment rate	0.200	0.273
Maximum | Discount rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Constant prepayment rate	0.140	0.130
Weighted Average | Constant prepayment rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Constant prepayment rate	0.176	0.076
Weighted Average | Discount rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Constant prepayment rate	0.120	0.120