Fair Value Measurement and Fair Value of Financial Instruments - Fair Value of Financial Assets and Liabilities Measured on Recurring Basis (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Assets:
Investment securities available for sale, at fair value	$ 783,331	$ 755,900
Equity securities, at fair value	14,076	16,473
U.S. Treasury and U.S. government agencies
Assets:
Investment securities available for sale, at fair value	73,275	135,647
Asset-backed securities
Assets:
Investment securities available for sale, at fair value	40,711	0
Obligations of states and political subdivisions
Assets:
Investment securities available for sale, at fair value	164,710	60,021
Fair Value, Measurements, Recurring
Assets:
Investment securities available for sale, at fair value	783,331	755,900
Equity securities, at fair value	14,076	16,473
Derivative assets	95,243	27,123
Total Assets	892,650	799,496
Liabilities:
Derivative liabilities	95,449	26,852
Total Liabilities	95,449	26,852
Fair Value, Measurements, Recurring \| U.S. Treasury and U.S. government agencies
Assets:
Investment securities available for sale, at fair value	73,275	135,647
Fair Value, Measurements, Recurring \| Mortgage-backed and asset-backed securities
Assets:
Investment securities available for sale, at fair value	476,827	551,064
Fair Value, Measurements, Recurring \| Asset-backed securities
Assets:
Investment securities available for sale, at fair value	40,711
Fair Value, Measurements, Recurring \| Obligations of states and political subdivisions
Assets:
Investment securities available for sale, at fair value	164,710	60,021
Fair Value, Measurements, Recurring \| Debt securities
Assets:
Investment securities available for sale, at fair value	27,808	9,168
Quoted Prices in Active Markets for Identical Assets (Level 1) \| Fair Value, Measurements, Recurring
Assets:
Investment securities available for sale, at fair value	10,955	12,580
Equity securities, at fair value	898	1,735
Derivative assets	0	0
Total Assets	11,853	14,315
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:
Investment securities available for sale, at fair value	10,955	12,580
Quoted Prices in Active Markets for Identical Assets (Level 1) \| Fair Value, Measurements, Recurring \| Mortgage-backed and asset-backed securities
Assets:
Investment securities available for sale, at fair value	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) \| Fair Value, Measurements, Recurring \| Asset-backed securities
Assets:
Investment securities available for sale, at fair value	0
Quoted Prices in Active Markets for Identical Assets (Level 1) \| Fair Value, Measurements, Recurring \| Obligations of states and political subdivisions
Assets:
Investment securities available for sale, at fair value	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) \| Fair Value, Measurements, Recurring \| Debt securities
Assets:
Investment securities available for sale, at fair value	0	0
Significant Other Observable Inputs (Level 2) \| Fair Value, Measurements, Recurring
Assets:
Investment securities available for sale, at fair value	772,376	743,320
Equity securities, at fair value	13,178	14,738
Derivative assets	95,243	27,123
Total Assets	880,797	785,181
Liabilities:
Derivative liabilities	95,449	26,852
Total Liabilities	95,449	26,852
Significant Other Observable Inputs (Level 2) \| Fair Value, Measurements, Recurring \| U.S. Treasury and U.S. government agencies
Assets:
Investment securities available for sale, at fair value	62,320	123,067
Significant Other Observable Inputs (Level 2) \| Fair Value, Measurements, Recurring \| Mortgage-backed and asset-backed securities
Assets:
Investment securities available for sale, at fair value	476,827	551,064
Significant Other Observable Inputs (Level 2) \| Fair Value, Measurements, Recurring \| Asset-backed securities
Assets:
Investment securities available for sale, at fair value	40,711
Significant Other Observable Inputs (Level 2) \| Fair Value, Measurements, Recurring \| Obligations of states and political subdivisions
Assets:
Investment securities available for sale, at fair value	164,710	60,021
Significant Other Observable Inputs (Level 2) \| Fair Value, Measurements, Recurring \| Debt securities
Assets:
Investment securities available for sale, at fair value	27,808	9,168
Significant Unobservable Inputs (Level 3) \| Fair Value, Measurements, Recurring
Assets:
Investment securities available for sale, at fair value	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:
Investment securities available for sale, at fair value	0	0
Significant Unobservable Inputs (Level 3) \| Fair Value, Measurements, Recurring \| Mortgage-backed and asset-backed securities
Assets:
Investment securities available for sale, at fair value	0	0
Significant Unobservable Inputs (Level 3) \| Fair Value, Measurements, Recurring \| Asset-backed securities
Assets:
Investment securities available for sale, at fair value	0
Significant Unobservable Inputs (Level 3) \| Fair Value, Measurements, Recurring \| Obligations of states and political subdivisions
Assets:
Investment securities available for sale, at fair value	0	0
Significant Unobservable Inputs (Level 3) \| Fair Value, Measurements, Recurring \| Debt securities
Assets:
Investment securities available for sale, at fair value	$ 0	$ 0

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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