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 ($)
Sep. 30, 2021
Dec. 31, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Securities available for sale $ 906,996,000 $ 753,781,000
Derivative financial instruments, Assets 800,000 1,100,000
Derivative financial instruments, Liabilities 769,000 1,100,000
U.S. Treasury securities    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Securities available for sale 4,945,000 10,132,000
Mortgage-backed securities    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Securities available for sale 636,062,000 519,241,000
Collateralized mortgage obligations    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Securities available for sale 99,883,000 133,601,000
Debt securities    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Securities available for sale 98,436,000 90,807,000
Total U.S. government agency and sponsored agency obligations    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Securities available for sale 834,381,000 743,649,000
Municipal bonds-tax exempt    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Securities available for sale 67,670,000  
Recurring Basis    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Securities available for sale 906,996,000 753,781,000
Recurring Basis | U.S. Treasury securities    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Securities available for sale 4,945,000 10,132,000
Recurring Basis | Mortgage-backed securities    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Securities available for sale 636,062,000 519,241,000
Recurring Basis | Collateralized mortgage obligations    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Securities available for sale 99,883,000 133,601,000
Recurring Basis | Debt securities    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Securities available for sale 98,436,000 90,807,000
Recurring Basis | Total U.S. government agency and sponsored agency obligations    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Securities available for sale 834,381,000 743,649,000
Recurring Basis | Derivative financial instruments    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Derivative financial instruments, Assets 800,000 1,088,000
Derivative financial instruments, Liabilities 769,000 1,149,000
Recurring Basis | Municipal bonds-tax exempt    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Securities available for sale 67,670,000  
Recurring Basis | Quoted Prices in Active Markets for Identical Assets    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Securities available for sale 4,945,000 10,132,000
Recurring Basis | 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]    
Securities available for sale 4,945,000 10,132,000
Recurring Basis | Quoted Prices in Active Markets for Identical Assets | Mortgage-backed securities    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Securities available for sale 0 0
Recurring Basis | Quoted Prices in Active Markets for Identical Assets | Collateralized mortgage obligations    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Securities available for sale 0 0
Recurring Basis | Quoted Prices in Active Markets for Identical Assets | Debt securities    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Securities available for sale 0 0
Recurring Basis | Quoted Prices in Active Markets for Identical Assets | Total U.S. government agency and sponsored agency obligations    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Securities available for sale 0 0
Recurring Basis | Quoted Prices in Active Markets for Identical Assets | Derivative financial instruments    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Derivative financial instruments, Assets 0 0
Derivative financial instruments, Liabilities 0 0
Recurring Basis | 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]    
Securities available for sale 0  
Recurring Basis | Significant Observable Inputs with No Active Market with Identical Characteristics    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Securities available for sale 902,051,000 743,649,000
Recurring Basis | 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]    
Securities available for sale 0 0
Recurring Basis | 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]    
Securities available for sale 636,062,000 519,241,000
Recurring Basis | 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]    
Securities available for sale 99,883,000 133,601,000
Recurring Basis | Significant Observable Inputs with No Active Market with Identical Characteristics | Debt securities    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Securities available for sale 98,436,000 90,807,000
Recurring Basis | Significant Observable Inputs with No Active Market with Identical Characteristics | Total U.S. government agency and sponsored agency obligations    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Securities available for sale 834,381,000 743,649,000
Recurring Basis | Significant Observable Inputs with No Active Market with Identical Characteristics | Derivative financial instruments    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Derivative financial instruments, Assets 800,000 1,088,000
Derivative financial instruments, Liabilities 769,000 1,149,000
Recurring Basis | 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]    
Securities available for sale 67,670,000  
Recurring Basis | Significant Unobservable Inputs    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Securities available for sale 0 0
Recurring Basis | Significant Unobservable Inputs | U.S. Treasury securities    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Securities available for sale 0 0
Recurring Basis | Significant Unobservable Inputs | Mortgage-backed securities    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Securities available for sale 0 0
Recurring Basis | Significant Unobservable Inputs | Collateralized mortgage obligations    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Securities available for sale 0 0
Recurring Basis | Significant Unobservable Inputs | Debt securities    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Securities available for sale 0 0
Recurring Basis | Significant Unobservable Inputs | Total U.S. government agency and sponsored agency obligations    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Securities available for sale 0 0
Recurring Basis | Significant Unobservable Inputs | Derivative financial instruments    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Derivative financial instruments, Assets 0 0
Derivative financial instruments, Liabilities 0 $ 0
Recurring Basis | Significant Unobservable Inputs | Municipal bonds-tax exempt    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Securities available for sale $ 0