Fair Value Measurement - Estimated Fair Values of Financial Instruments that are Reported at Amortized Cost in Consolidated Balance Sheets (Detail) - USD ($)	Sep. 30, 2017	Dec. 31, 2016
Financial assets:
Cash and due from banks	$ 86,815,000	$ 92,197,000
Cash at Federal Reserve and other banks	101,219,000	213,415,000
Securities held to maturity	536,567,000	602,536,000
Financial liabilities:
Other borrowings	98,730,000	17,493,000
Junior subordinated debt	56,810,000	56,667,000
Level 3 [Member]
Financial assets:
Securities held to maturity	0	0
Level 3 [Member] | Overdraft Privilege Commitments [Member]
Off-balance sheet:
Contract amount, Off-balance sheet	96,650,000	98,583,000
Level 3 [Member] | Standby Letters of Credit [Member]
Off-balance sheet:
Contract amount, Off-balance sheet	12,700,000	12,763,000
Level 3 [Member] | Commitments [Member]
Off-balance sheet:
Contract amount, Off-balance sheet	909,900,000	767,274,000
Fair Value [Member] | Level 3 [Member]
Financial assets:
Loans, net	2,928,059,000	2,763,473,000
Financial liabilities:
Junior subordinated debt	55,259,000	49,033,000
Fair Value [Member] | Level 3 [Member] | Overdraft Privilege Commitments [Member]
Off-balance sheet:
Fair value, Off-balance sheet	967,000	986,000
Fair Value [Member] | Level 3 [Member] | Standby Letters of Credit [Member]
Off-balance sheet:
Fair value, Off-balance sheet	128,000	128,000
Fair Value [Member] | Level 3 [Member] | Commitments [Member]
Off-balance sheet:
Fair value, Off-balance sheet	9,099,000	7,673,000
Fair Value [Member] | Level 1 [Member]
Financial assets:
Cash and due from banks	86,815,000	92,197,000
Cash at Federal Reserve and other banks	101,219,000	213,415,000
Fair Value [Member] | Level 2 [Member]
Financial assets:
Securities held to maturity	542,123,000	603,203,000
Loans held for sale	2,733,000	2,998,000
Financial liabilities:
Deposits	3,925,527,000	3,893,941,000
Other borrowings	98,730,000	17,493,000
Carrying Amount [Member] | Level 3 [Member]
Financial assets:
Loans, net	2,902,866,000	2,727,090,000
Financial liabilities:
Junior subordinated debt	56,810,000	56,667,000
Carrying Amount [Member] | Level 1 [Member]
Financial assets:
Cash and due from banks	86,815,000	92,197,000
Cash at Federal Reserve and other banks	101,219,000	213,415,000
Carrying Amount [Member] | Level 2 [Member]
Financial assets:
Securities held to maturity	536,567,000	602,536,000
Restricted equity securities	16,956,000	16,956,000
Loans held for sale	2,733,000	2,998,000
Financial liabilities:
Deposits	3,927,456,000	3,895,560,000
Other borrowings	$ 98,730,000	$ 17,493,000