Fair Value Measurement - Quantitative Information about (Level 3) Fair Value Measurements for Financial Instruments Measured at Fair Value on Nonrecurring Basis (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Impaired Originated & PNCI Loans
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	$ 1,055	$ 281
Foreclosed Assets | Residential Real Estate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	$ 417	693
Foreclosed Assets | Commercial Real Estate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value		$ 618
Level 3 | Sales Comparison Approach | Minimum | Impaired Originated & PNCI Loans | Adjustment for Differences between Comparable Sales
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Weighted average		(16.30%)
Level 3 | Sales Comparison Approach | Minimum | Foreclosed Assets | Residential Real Estate | Adjustment for Differences between Comparable Sales
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Weighted average		(21.83%)
Level 3 | Sales Comparison Approach | Minimum | Foreclosed Assets | Commercial Real Estate | Adjustment for Differences between Comparable Sales
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Weighted average		(65.00%)
Level 3 | Sales Comparison Approach | Maximum | Impaired Originated & PNCI Loans | Adjustment for Differences between Comparable Sales
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Weighted average		35.14%
Level 3 | Sales Comparison Approach | Maximum | Foreclosed Assets | Residential Real Estate | Adjustment for Differences between Comparable Sales
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Weighted average		7.25%
Level 3 | Sales Comparison Approach | Maximum | Foreclosed Assets | Commercial Real Estate | Adjustment for Differences between Comparable Sales
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Weighted average		20.00%
Level 3 | Sales Comparison Approach | Weighted Average | Impaired Originated & PNCI Loans | Adjustment for Differences between Comparable Sales
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Weighted average		10.45%
Level 3 | Sales Comparison Approach | Weighted Average | Foreclosed Assets | Residential Real Estate | Adjustment for Differences between Comparable Sales
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Weighted average		(3.75%)
Level 3 | Sales Comparison Approach | Weighted Average | Foreclosed Assets | Commercial Real Estate | Adjustment for Differences between Comparable Sales
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Weighted average		(45.00%)