Fair Value Measurements - Financial Instruments Measured at Fair Value on a Recurring and Non-recurring Basis (Detail) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities AFS	$ 410,214	$ 448,390
Fair Value Measurements, Level 1 Inputs [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities AFS	277	296
Fair Value Measurements, Level 2 Inputs [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities AFS	262,801	351,208
Fair Value Measurements, Level 3 Inputs [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities AFS	147,136	96,886
Financial Instruments Measured at Fair Value on a Non-recurring Basis
Impaired Loans	1,131	3,410
U.S. Treasury [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities AFS	1,998	2,000
U.S. Treasury [Member] | Fair Value Measurements, Level 2 Inputs [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities AFS	1,998	2,000
Small Business Administration [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities AFS	6,413	6,717
Small Business Administration [Member] | Fair Value Measurements, Level 2 Inputs [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities AFS	6,413	6,717
U.S. Government Agency and Sponsored Mortgage Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities AFS	249,349	337,093
U.S. Government Agency and Sponsored Mortgage Backed Securities [Member] | Fair Value Measurements, Level 2 Inputs [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities AFS	249,349	337,093
Privately Issued Residential Mortgage Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities AFS	1,528	1,874
Privately Issued Residential Mortgage Backed Securities [Member] | Fair Value Measurements, Level 2 Inputs [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities AFS	1,528	1,874
Obligations Issued by States and Political Subdivisions [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities AFS	147,099	96,784
Obligations Issued by States and Political Subdivisions [Member] | Fair Value Measurements, Level 3 Inputs [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities AFS	147,099	96,784
Other Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities AFS	3,513	3,524
Other Debt Securities [Member] | Fair Value Measurements, Level 2 Inputs [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities AFS	3,513	3,524
Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities AFS	314	398
Equity Securities [Member] | Fair Value Measurements, Level 1 Inputs [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities AFS	277	296
Equity Securities [Member] | Fair Value Measurements, Level 3 Inputs [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities AFS	37	102
Carrying Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities AFS	410,214	448,390
Financial Instruments Measured at Fair Value on a Non-recurring Basis
Impaired Loans	1,131	3,410
Carrying Value [Member] | U.S. Treasury [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities AFS	1,998	2,000
Carrying Value [Member] | Small Business Administration [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities AFS	6,413	6,717
Carrying Value [Member] | U.S. Government Agency and Sponsored Mortgage Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities AFS	249,349	337,093
Carrying Value [Member] | Privately Issued Residential Mortgage Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities AFS	1,528	1,874
Carrying Value [Member] | Obligations Issued by States and Political Subdivisions [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities AFS	147,099	96,784
Carrying Value [Member] | Other Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities AFS	3,513	3,524
Carrying Value [Member] | Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities AFS	$ 314	$ 398