Fair Value Measurement - Quantitative Information about Recurring Fair Value Measurements (Detail) $ in Thousands	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	$ 6,200	$ 7,098
Mortgage servicing rights
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	$ 6,200	$ 7,098	$ 6,687	$ 6,595
Minimum | Constant prepayment rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Constant prepayment rate	0.273	0.420
Minimum | Discount rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Constant prepayment rate	0.12	0.140
Maximum | Constant prepayment rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Constant prepayment rate	0.076	0.110
Maximum | Discount rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Constant prepayment rate	0.13	0.120
Weighted Average | Constant prepayment rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Constant prepayment rate	0.050	0.062
Weighted Average | Discount rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Constant prepayment rate	0.12	0.100