Fair Value Measurement and Fair Value of Financial Instruments - Fair Value of Financial Assets and Liabilities Measured on Recurring Basis (Detail) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Assets:
Total securities	$ 968,394	$ 855,746
Equity securities, at fair value	14,590	14,694
U.S. Treasury and U.S. government agencies
Assets:
Total securities	93,033	65,002
Asset-backed securities
Assets:
Total securities	40,187	40,690
Obligations of states and political subdivisions
Assets:
Total securities	255,122	233,710
Fair Value, Measurements, Recurring
Assets:
Total securities	968,394	855,746
Equity securities, at fair value	14,590	14,694
Derivative assets	52,725	80,734
Total Assets	1,035,709	951,174
Liabilities:
Derivative liabilities	52,801	80,877
Total Liabilities	52,801	80,877
Fair Value, Measurements, Recurring | U.S. Treasury and U.S. government agencies
Assets:
Total securities	93,033	65,002
Fair Value, Measurements, Recurring | Mortgage-backed and asset-backed securities
Assets:
Total securities	325,831	230,100
Fair Value, Measurements, Recurring | Collateralized mortgage obligations
Assets:
Total securities	218,669	250,573
Fair Value, Measurements, Recurring | Asset-backed securities
Assets:
Total securities	40,187	40,690
Fair Value, Measurements, Recurring | Obligations of states and political subdivisions
Assets:
Total securities	255,122	233,710
Fair Value, Measurements, Recurring | Debt securities
Assets:
Total securities	35,552	35,671
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value, Measurements, Recurring
Assets:
Total securities	7,742	9,392
Equity securities, at fair value	0	0
Derivative assets	0	0
Total Assets	7,742	9,392
Liabilities:
Derivative liabilities	0	0
Total Liabilities	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value, Measurements, Recurring | U.S. Treasury and U.S. government agencies
Assets:
Total securities	7,742	9,392
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value, Measurements, Recurring | Mortgage-backed and asset-backed securities
Assets:
Total securities	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value, Measurements, Recurring | Collateralized mortgage obligations
Assets:
Total securities	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value, Measurements, Recurring | Asset-backed securities
Assets:
Total securities	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value, Measurements, Recurring | Obligations of states and political subdivisions
Assets:
Total securities	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value, Measurements, Recurring | Debt securities
Assets:
Total securities	0	0
Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring
Assets:
Total securities	960,652	846,354
Equity securities, at fair value	14,590	14,694
Derivative assets	52,725	80,734
Total Assets	1,027,967	941,782
Liabilities:
Derivative liabilities	52,801	80,877
Total Liabilities	52,801	80,877
Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring | U.S. Treasury and U.S. government agencies
Assets:
Total securities	85,291	55,610
Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring | Mortgage-backed and asset-backed securities
Assets:
Total securities	325,831	230,100
Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring | Collateralized mortgage obligations
Assets:
Total securities	218,669	250,573
Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring | Asset-backed securities
Assets:
Total securities	40,187	40,690
Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring | Obligations of states and political subdivisions
Assets:
Total securities	255,122	233,710
Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring | Debt securities
Assets:
Total securities	35,552	35,671
Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring
Assets:
Total securities	0	0
Equity securities, at fair value	0	0
Derivative assets	0	0
Total Assets	0	0
Liabilities:
Derivative liabilities	0	0
Total Liabilities	0	0
Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring | U.S. Treasury and U.S. government agencies
Assets:
Total securities	0	0
Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring | Mortgage-backed and asset-backed securities
Assets:
Total securities	0	0
Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring | Collateralized mortgage obligations
Assets:
Total securities	0	0
Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring | Asset-backed securities
Assets:
Total securities	0	0
Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring | Obligations of states and political subdivisions
Assets:
Total securities	0	0
Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring | Debt securities
Assets:
Total securities	$ 0	$ 0