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	9 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Impaired Originated & PNCI Loans [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	$ 1,026	$ 1,107
Foreclosed Assets [Member] | Land & Construction [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	960	15
Foreclosed Assets [Member] | Residential Real Estate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	822	1,564
Foreclosed Assets [Member] | Commercial Real Estate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	$ 280	$ 674
Level 3 [Member] | Sales Comparison Approach [Member] | Minimum [Member] | Impaired Originated & PNCI Loans [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Adjustment for differences between comparable sales	(74.00%)
Level 3 [Member] | Sales Comparison Approach [Member] | Minimum [Member] | Foreclosed Assets [Member] | Land & Construction [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Adjustment for differences between comparable sales	(53.00%)
Level 3 [Member] | Sales Comparison Approach [Member] | Minimum [Member] | Foreclosed Assets [Member] | Residential Real Estate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Adjustment for differences between comparable sales	(47.00%)
Level 3 [Member] | Sales Comparison Approach [Member] | Minimum [Member] | Foreclosed Assets [Member] | Commercial Real Estate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Adjustment for differences between comparable sales	(46.00%)
Level 3 [Member] | Sales Comparison Approach [Member] | Maximum [Member] | Impaired Originated & PNCI Loans [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Adjustment for differences between comparable sales	21.00%
Level 3 [Member] | Sales Comparison Approach [Member] | Maximum [Member] | Foreclosed Assets [Member] | Land & Construction [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Adjustment for differences between comparable sales	283.00%
Level 3 [Member] | Sales Comparison Approach [Member] | Maximum [Member] | Foreclosed Assets [Member] | Residential Real Estate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Adjustment for differences between comparable sales	39.00%
Level 3 [Member] | Sales Comparison Approach [Member] | Maximum [Member] | Foreclosed Assets [Member] | Commercial Real Estate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Adjustment for differences between comparable sales	63.00%
Level 3 [Member] | Sales Comparison Approach [Member] | Weighted Average [Member] | Impaired Originated & PNCI Loans [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Adjustment for differences between comparable sales	(32.00%)
Level 3 [Member] | Sales Comparison Approach [Member] | Weighted Average [Member] | Foreclosed Assets [Member] | Land & Construction [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Adjustment for differences between comparable sales	230.00%
Level 3 [Member] | Sales Comparison Approach [Member] | Weighted Average [Member] | Foreclosed Assets [Member] | Residential Real Estate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Adjustment for differences between comparable sales	3.30%
Level 3 [Member] | Sales Comparison Approach [Member] | Weighted Average [Member] | Foreclosed Assets [Member] | Commercial Real Estate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Adjustment for differences between comparable sales	26.00%
Level 3 [Member] | Income Approach [Member] | Minimum [Member] | Impaired Originated & PNCI Loans [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Capitalization rate	0.00%
Level 3 [Member] | Income Approach [Member] | Maximum [Member] | Impaired Originated & PNCI Loans [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Capitalization rate	0.00%
Level 3 [Member] | Income Approach [Member] | Weighted Average [Member] | Impaired Originated & PNCI Loans [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Capitalization rate	0.00%