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	12 Months Ended
	Sep. 30, 2015	Dec. 31, 2014	Sep. 30, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	$ 6,622	$ 5,091	$ 6,102
Impaired Originated & PNCI loans [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	4,399	2,480	3,090
Foreclosed assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	2,223	2,611	3,012
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	6,622	5,091	6,102
Level 3 [Member] | Impaired Originated & PNCI loans [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	4,399	2,480	3,090
Level 3 [Member] | Foreclosed assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	$ 2,223	$ 2,611	$ 3,012
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	(5.00%)	(5.00%)
Level 3 [Member] | Sales comparison approach [Member] | Minimum [Member] | Foreclosed assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Adjustment for differences between comparable sales	(5.00%)	(5.00%)
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	(5.00%)	(42.50%)
Level 3 [Member] | Sales comparison approach [Member] | Maximum [Member] | Foreclosed assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Adjustment for differences between comparable sales	(12.00%)	(29.40%)
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	(5.00%)	(10.10%)
Level 3 [Member] | Sales comparison approach [Member] | Weighted Average [Member] | Foreclosed assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Adjustment for differences between comparable sales	(6.20%)	(8.20%)
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	7.00%	9.09%
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	8.00%	9.09%
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	7.30%	9.09%