Fair Value Measurement - Quantitative Information about Recurring Level 3 Fair Value Measurements (Detail) - Mortgage Servicing Rights $ in Thousands	Sep. 30, 2019 USD ($)	Dec. 31, 2018 USD ($)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Mortgages Servicing Rights, Fair Value	$ 6,072	$ 7,098
Minimum | Valuation Technique, Discounted Cash Flow | Measurement Input, Constant Prepayment Rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Constant prepayment rate	0.07	0.05
Minimum | Valuation Technique, Discounted Cash Flow | Measurement Input, Discount Rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Constant prepayment rate	0.10	0.12
Maximum | Valuation Technique, Discounted Cash Flow | Measurement Input, Constant Prepayment Rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Constant prepayment rate	0.42	0.273
Maximum | Valuation Technique, Discounted Cash Flow | Measurement Input, Discount Rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Constant prepayment rate	0.14	0.13
Weighted Average | Valuation Technique, Discounted Cash Flow | Measurement Input, Constant Prepayment Rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Constant prepayment rate	0.11	0.076
Weighted Average | Valuation Technique, Discounted Cash Flow | Measurement Input, Discount Rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Constant prepayment rate	0.12	0.12