Quarterly report pursuant to Section 13 or 15(d)

Fair Value Measurements - Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail)

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Fair Value Measurements - Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($)
$ in Thousands
Sep. 30, 2017
Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Securities available for sale $ 598,440 $ 516,964
Recurring Basis [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Securities available for sale 598,440 516,964
Recurring Basis [Member] | Mortgage-backed securities [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Securities available for sale 309,750 229,630
Recurring Basis [Member] | Collateralized mortgage obligations [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Securities available for sale 106,124 76,451
Recurring Basis [Member] | U.S. government agency securities [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Securities available for sale 7,457 7,441
Recurring Basis [Member] | SBA loan pools securities [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Securities available for sale 3,896 4,146
Recurring Basis [Member] | Municipal bonds-tax exempt [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Securities available for sale 148,524 158,030
Recurring Basis [Member] | Municipal bonds-taxable [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Securities available for sale   13,701
Recurring Basis [Member] | Corporate bonds [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Securities available for sale   5,015
Recurring Basis [Member] | U.S treasury securities [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Securities available for sale 153 156
Recurring Basis [Member] | Mutual funds [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Securities available for sale 22,536 22,394
Recurring Basis [Member] | Fair Value, Inputs, Level 2 [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Securities available for sale 575,751 494,414
Recurring Basis [Member] | Fair Value, Inputs, Level 2 [Member] | Mortgage-backed securities [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Securities available for sale 309,750 229,630
Recurring Basis [Member] | Fair Value, Inputs, Level 2 [Member] | Collateralized mortgage obligations [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Securities available for sale 106,124 76,451
Recurring Basis [Member] | Fair Value, Inputs, Level 2 [Member] | U.S. government agency securities [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Securities available for sale 7,457 7,441
Recurring Basis [Member] | Fair Value, Inputs, Level 2 [Member] | SBA loan pools securities [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Securities available for sale 3,896 4,146
Recurring Basis [Member] | Fair Value, Inputs, Level 2 [Member] | Municipal bonds-tax exempt [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Securities available for sale 148,524 158,030
Recurring Basis [Member] | Fair Value, Inputs, Level 2 [Member] | Municipal bonds-taxable [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Securities available for sale   13,701
Recurring Basis [Member] | Fair Value, Inputs, Level 2 [Member] | Corporate bonds [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Securities available for sale   5,015
Recurring Basis [Member] | Fair Value, Inputs, Level 2 [Member] | U.S treasury securities [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Securities available for sale 0 0
Recurring Basis [Member] | Fair Value, Inputs, Level 2 [Member] | Mutual funds [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Securities available for sale 0 0
Recurring Basis [Member] | Fair Value, Inputs, Level 3 [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Securities available for sale 0 0
Recurring Basis [Member] | Fair Value, Inputs, Level 3 [Member] | Mortgage-backed securities [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Securities available for sale 0 0
Recurring Basis [Member] | Fair Value, Inputs, Level 3 [Member] | Collateralized mortgage obligations [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Securities available for sale 0 0
Recurring Basis [Member] | Fair Value, Inputs, Level 3 [Member] | U.S. government agency securities [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Securities available for sale 0 0
Recurring Basis [Member] | Fair Value, Inputs, Level 3 [Member] | SBA loan pools securities [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Securities available for sale 0 0
Recurring Basis [Member] | Fair Value, Inputs, Level 3 [Member] | Municipal bonds-tax exempt [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Securities available for sale 0 0
Recurring Basis [Member] | Fair Value, Inputs, Level 3 [Member] | Municipal bonds-taxable [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Securities available for sale   0
Recurring Basis [Member] | Fair Value, Inputs, Level 3 [Member] | Corporate bonds [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Securities available for sale   0
Recurring Basis [Member] | Fair Value, Inputs, Level 3 [Member] | U.S treasury securities [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Securities available for sale 0 0
Recurring Basis [Member] | Fair Value, Inputs, Level 3 [Member] | Mutual funds [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Securities available for sale 0 0
Recurring Basis [Member] | Fair Value, Inputs, Level 1 [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Securities available for sale 22,689 22,550
Recurring Basis [Member] | Fair Value, Inputs, Level 1 [Member] | Mortgage-backed securities [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Securities available for sale 0 0
Recurring Basis [Member] | Fair Value, Inputs, Level 1 [Member] | Collateralized mortgage obligations [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Securities available for sale 0 0
Recurring Basis [Member] | Fair Value, Inputs, Level 1 [Member] | U.S. government agency securities [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Securities available for sale 0 0
Recurring Basis [Member] | Fair Value, Inputs, Level 1 [Member] | SBA loan pools securities [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Securities available for sale 0 0
Recurring Basis [Member] | Fair Value, Inputs, Level 1 [Member] | Municipal bonds-tax exempt [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Securities available for sale 0 0
Recurring Basis [Member] | Fair Value, Inputs, Level 1 [Member] | Municipal bonds-taxable [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Securities available for sale   0
Recurring Basis [Member] | Fair Value, Inputs, Level 1 [Member] | Corporate bonds [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Securities available for sale   0
Recurring Basis [Member] | Fair Value, Inputs, Level 1 [Member] | U.S treasury securities [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Securities available for sale 153 156
Recurring Basis [Member] | Fair Value, Inputs, Level 1 [Member] | Mutual funds [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Securities available for sale $ 22,536 $ 22,394