Fair Value Measurement - Quantitative Information about Recurring Level 3 Fair Value Measurements (Detail) - Mortgage Servicing Rights [Member] $ in Thousands	Jun. 30, 2019 USD ($)	Dec. 31, 2018 USD ($)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Mortgages Servicing Rights, Fair Value	$ 6,229	$ 7,098
Minimum [Member] | Valuation Technique, Discounted Cash Flow [Member] | Measurement Input, Constant Prepayment Rate [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Constant prepayment rate	6.9	5.0
Minimum [Member] | Valuation Technique, Discounted Cash Flow [Member] | Measurement Input, Discount Rate [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Constant prepayment rate	10	12
Maximum [Member] | Valuation Technique, Discounted Cash Flow [Member] | Measurement Input, Constant Prepayment Rate [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Constant prepayment rate	39.0	27.3
Maximum [Member] | Valuation Technique, Discounted Cash Flow [Member] | Measurement Input, Discount Rate [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Constant prepayment rate	14	13
Weighted Average [Member] | Valuation Technique, Discounted Cash Flow [Member] | Measurement Input, Constant Prepayment Rate [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Constant prepayment rate	10.5	7.6
Weighted Average [Member] | Valuation Technique, Discounted Cash Flow [Member] | Measurement Input, Discount Rate [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Constant prepayment rate	12	12