Fair Value Measurement - Estimated Fair Values of Financial Instruments that are Reported at Amortized Cost in Consolidated Balance Sheets (Detail) - USD ($)	Dec. 31, 2020	Dec. 31, 2019
Financial assets:
Cash and due from banks	$ 77,253,000	$ 92,816,000
Cash at Federal Reserve and other banks	592,298,000	183,691,000
Securities held to maturity	284,563,000	375,606,000
Restricted equity securities	0	0
Financial liabilities:
Other borrowings	26,914,000	18,454,000
Junior subordinated debt	57,635,000	57,232,000
Level 3 | Overdraft privilege commitments (1)
Off-balance sheet:
Contract amount, Off-balance sheet	110,813,000	110,402,000
Level 3 | Standby letters of credit (1)
Off-balance sheet:
Contract amount, Off-balance sheet	15,056,000	12,014,000
Level 3 | Commitments (1)
Off-balance sheet:
Contract amount, Off-balance sheet	1,426,827,000	1,309,326,000
Fair Value | Level 1
Financial assets:
Cash and due from banks	77,253,000	92,816,000
Cash at Federal Reserve and other banks	592,298,000	183,691,000
Fair Value | Level 2
Financial assets:
Securities held to maturity	298,726,000	381,525,000
Financial liabilities:
Deposits	6,507,235,000	5,365,921,000
Other borrowings	26,914,000	18,454,000
Fair Value | Level 3
Financial assets:
Loans, net	4,753,027,000	4,263,064,000
Financial liabilities:
Junior subordinated debt	56,632,000	56,297,000
Fair Value | Level 3 | Overdraft privilege commitments (1)
Off-balance sheet:
Fair value, Off-balance sheet	1,108,000	1,104,000
Fair Value | Level 3 | Standby letters of credit (1)
Off-balance sheet:
Fair value, Off-balance sheet	151,000	120,000
Fair Value | Level 3 | Commitments (1)
Off-balance sheet:
Fair value, Off-balance sheet	14,268,000	13,093,000
Carrying Amount | Level 1
Financial assets:
Cash and due from banks	77,253,000	92,816,000
Cash at Federal Reserve and other banks	592,298,000	183,691,000
Carrying Amount | Level 2
Financial assets:
Securities held to maturity	284,563,000	375,606,000
Restricted equity securities	17,250,000	17,250,000
Financial liabilities:
Deposits	6,505,934,000	5,366,994,000
Other borrowings	26,914,000	18,454,000
Carrying Amount | Level 3
Financial assets:
Loans, net	4,671,280,000	4,276,750,000
Financial liabilities:
Junior subordinated debt	$ 57,635,000	$ 57,232,000