Fair Value Measurement and Fair Value of Financial Instruments - Fair Value of Financial Assets and Liabilities Measured on Recurring Basis (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities, available for sale, at fair value	$ 755,900	$ 638,618
Assets:
Equity securities, at fair value	16,473	15,921
Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities, available for sale, at fair value	755,900	638,618
Assets:
Equity securities, at fair value	16,473	15,921
Derivative assets	27,123	12,135
Total Assets	799,496	666,674
Liabilities:
Total Liabilities	26,852	11,036
Fair Value, Measurements, Recurring | Non Hedging
Liabilities:
Derivative liabilities	26,852	11,036
Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities, available for sale, at fair value	743,320	633,698
Assets:
Equity securities, at fair value	14,738	13,190
Derivative assets	27,123	12,135
Total Assets	785,181	659,023
Liabilities:
Total Liabilities	26,852	11,036
Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring | Non Hedging
Liabilities:
Derivative liabilities	26,852	11,036
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities, available for sale, at fair value	12,580	4,920
Assets:
Equity securities, at fair value	1,735	2,731
Derivative assets	0	0
Total Assets	14,315	7,651
Liabilities:
Total Liabilities	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value, Measurements, Recurring | Non Hedging
Liabilities:
Derivative liabilities	0	0
Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities, available for sale, at fair value	0	0
Assets:
Equity securities, at fair value	0	0
Derivative assets	0	0
Total Assets	0	0
Liabilities:
Total Liabilities	0	0
Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring | Non Hedging
Liabilities:
Derivative liabilities	0	0
U.S. Treasury and U.S. government agencies
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities, available for sale, at fair value	135,647	140,927
U.S. Treasury and U.S. government agencies | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities, available for sale, at fair value	135,647	140,927
U.S. Treasury and U.S. government agencies | Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities, available for sale, at fair value	123,067	136,007
U.S. Treasury and U.S. government agencies | Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities, available for sale, at fair value	12,580	4,920
U.S. Treasury and U.S. government agencies | Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities, available for sale, at fair value	0	0
Mortgage-backed securities | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities, available for sale, at fair value	551,064	447,094
Mortgage-backed securities | Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities, available for sale, at fair value	551,064	447,094
Mortgage-backed securities | Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities, available for sale, at fair value	0	0
Mortgage-backed securities | Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities, available for sale, at fair value	0	0
Obligations of states and political subdivisions
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities, available for sale, at fair value	60,021	45,505
Obligations of states and political subdivisions | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities, available for sale, at fair value	60,021	45,505
Obligations of states and political subdivisions | Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities, available for sale, at fair value	60,021	45,505
Obligations of states and political subdivisions | Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities, available for sale, at fair value	0	0
Obligations of states and political subdivisions | Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities, available for sale, at fair value	0	0
Corporate debt securities | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities, available for sale, at fair value	9,168	5,092
Corporate debt securities | Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities, available for sale, at fair value	9,168	5,092
Corporate debt securities | Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities, available for sale, at fair value	0	0
Corporate debt securities | Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities, available for sale, at fair value	$ 0	$ 0