Summary of Financial Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($)
$ in Thousands
Sep. 30, 2016
Dec. 31, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total available-for-sale securities $ 220,856 $ 366,173
Derivative Liabilities 450 251
Municipal securities    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total available-for-sale securities 122,074 128,678
Recurring    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total available-for-sale securities 220,856 366,173
Fair value loans 4,464 4,886
Deferred compensation assets 3,842 3,464
Deferred compensation liabilities 3,842 3,464
Derivative Liabilities 450 251
Recurring | Municipal securities    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total available-for-sale securities 122,074 128,678
Recurring | U.S. Agency securities    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total available-for-sale securities 1,375 30,702
Recurring | Single Issue Trust Preferred Securities    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total available-for-sale securities 48,520 47,832
Recurring | Corporate securities    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total available-for-sale securities 15,022 70,333
Recurring | Certificates of deposit    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total available-for-sale securities   5,000
Recurring | Agency Mortgage Backed Securities    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total available-for-sale securities 33,792 83,556
Recurring | Equity Securities    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total available-for-sale securities 73 72
Level 1    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total available-for-sale securities 55 54
Deferred compensation assets 3,842 3,464
Deferred compensation liabilities 3,842 3,464
Level 1 | Recurring    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total available-for-sale securities 55 54
Deferred compensation assets 3,842 3,464
Deferred compensation liabilities 3,842 3,464
Level 1 | Recurring | Equity Securities    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total available-for-sale securities 55 54
Level 2    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total available-for-sale securities 220,801 366,119
Fair value loans 4,464 4,886
Derivative Liabilities 450 251
Level 2 | Recurring    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total available-for-sale securities 220,801 366,119
Fair value loans 4,464 4,886
Derivative Liabilities 450 251
Level 2 | Recurring | Municipal securities    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total available-for-sale securities 122,074 128,678
Level 2 | Recurring | U.S. Agency securities    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total available-for-sale securities 1,375 30,702
Level 2 | Recurring | Single Issue Trust Preferred Securities    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total available-for-sale securities 48,520 47,832
Level 2 | Recurring | Corporate securities    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total available-for-sale securities 15,022 70,333
Level 2 | Recurring | Certificates of deposit    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total available-for-sale securities   5,000
Level 2 | Recurring | Agency Mortgage Backed Securities    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total available-for-sale securities 33,792 83,556
Level 2 | Recurring | Equity Securities    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total available-for-sale securities $ 18 $ 18