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, 2018
Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Securities available for sale $ 572,236 $ 578,804
Mortgage-backed securities [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Securities available for sale 298,386 303,609
Collateralized mortgage obligations [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Securities available for sale 117,655 117,768
U.S. government agency securities [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Securities available for sale 7,352 7,414
Municipal bonds-tax exempt [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Securities available for sale 109,278 127,475
U.S treasury securities [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Securities available for sale 39,565 152
Mutual funds [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Securities available for sale   22,386
Recurring Basis [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Securities available for sale 572,236 578,804
Recurring Basis [Member] | Mortgage-backed securities [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Securities available for sale 298,386 303,609
Recurring Basis [Member] | Collateralized mortgage obligations [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Securities available for sale 117,655 117,768
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 7,352 7,414
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 109,278 127,475
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 39,565 152
Recurring Basis [Member] | Mutual funds [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Securities available for sale   22,386
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 39,565 22,538
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] | 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] | U.S treasury securities [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Securities available for sale 39,565 152
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   22,386
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 532,671 556,266
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 298,386 303,609
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 117,655 117,768
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 7,352 7,414
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 109,278 127,475
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
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] | 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] | 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