Annual report pursuant to Section 13 and 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
Dec. 31, 2018
Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Estimated Fair Value $ 574,908 $ 578,804
Collateralized mortgage obligations    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Estimated Fair Value 122,292 117,768
U.S. government agency securities    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Estimated Fair Value 7,402 7,414
Municipal bonds-tax exempt    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Estimated Fair Value 110,350 127,475
Mutual funds    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Estimated Fair Value   22,386
Recurring Basis [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Estimated Fair Value 574,908 578,804
Recurring Basis [Member] | Mortgage-backed securities    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Estimated Fair Value 295,034 303,609
Recurring Basis [Member] | Collateralized mortgage obligations    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Estimated Fair Value 122,292 117,768
Recurring Basis [Member] | U.S. government agency securities    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Estimated Fair Value 7,402 7,414
Recurring Basis [Member] | Municipal bonds-tax exempt    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Estimated Fair Value 110,350 127,475
Recurring Basis [Member] | U.S. treasury securities    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Estimated Fair Value 39,830 152
Recurring Basis [Member] | Mutual funds    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Estimated Fair Value   22,386
Recurring Basis [Member] | Quoted Prices in Active Markets for Identical Assets    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Estimated Fair Value 39,830 22,538
Recurring Basis [Member] | Quoted Prices in Active Markets for Identical Assets | Mortgage-backed securities    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Estimated Fair Value 0 0
Recurring Basis [Member] | Quoted Prices in Active Markets for Identical Assets | Collateralized mortgage obligations    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Estimated Fair Value 0 0
Recurring Basis [Member] | Quoted Prices in Active Markets for Identical Assets | U.S. government agency securities    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Estimated Fair Value 0 0
Recurring Basis [Member] | Quoted Prices in Active Markets for Identical Assets | Municipal bonds-tax exempt    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Estimated Fair Value 0 0
Recurring Basis [Member] | Quoted Prices in Active Markets for Identical Assets | U.S. treasury securities    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Estimated Fair Value 39,830 152
Recurring Basis [Member] | Quoted Prices in Active Markets for Identical Assets | Mutual funds    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Estimated Fair Value   22,386
Recurring Basis [Member] | Significant Observable Inputs with No Active Market with Identical Characteristics    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Estimated Fair Value 535,078 556,266
Recurring Basis [Member] | Significant Observable Inputs with No Active Market with Identical Characteristics | Mortgage-backed securities    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Estimated Fair Value 295,034 303,609
Recurring Basis [Member] | Significant Observable Inputs with No Active Market with Identical Characteristics | Collateralized mortgage obligations    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Estimated Fair Value 122,292 117,768
Recurring Basis [Member] | Significant Observable Inputs with No Active Market with Identical Characteristics | U.S. government agency securities    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Estimated Fair Value 7,402 7,414
Recurring Basis [Member] | Significant Observable Inputs with No Active Market with Identical Characteristics | Municipal bonds-tax exempt    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Estimated Fair Value 110,350 127,475
Recurring Basis [Member] | Significant Observable Inputs with No Active Market with Identical Characteristics | U.S. treasury securities    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Estimated Fair Value 0 0
Recurring Basis [Member] | Significant Observable Inputs with No Active Market with Identical Characteristics | Mutual funds    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Estimated Fair Value   0
Recurring Basis [Member] | Significant Unobservable Inputs    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Estimated Fair Value 0 0
Recurring Basis [Member] | Significant Unobservable Inputs | Mortgage-backed securities    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Estimated Fair Value 0 0
Recurring Basis [Member] | Significant Unobservable Inputs | Collateralized mortgage obligations    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Estimated Fair Value 0 0
Recurring Basis [Member] | Significant Unobservable Inputs | U.S. government agency securities    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Estimated Fair Value 0 0
Recurring Basis [Member] | Significant Unobservable Inputs | Municipal bonds-tax exempt    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Estimated Fair Value 0 0
Recurring Basis [Member] | Significant Unobservable Inputs | U.S. treasury securities    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Estimated Fair Value $ 0 0
Recurring Basis [Member] | Significant Unobservable Inputs | Mutual funds    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Estimated Fair Value   $ 0