Fair Value Measurement - Estimated Fair Values of Financial Instruments that are Reported at Amortized Cost in Consolidated Balance Sheets (Detail) - USD ($)	Dec. 31, 2016	Dec. 31, 2015
Financial assets:
Cash and due from banks	$ 92,197,000	$ 94,305,000
Cash at Federal Reserve and other banks	213,415,000	209,156,000
Securities held to maturity	602,536,000	726,530,000
Financial liabilities:
Other borrowings	17,493,000	12,328,000
Junior subordinated debt	56,667,000	56,470,000
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	98,583,000	94,473,000
Level 3 [Member] | Standby Letters of Credit [Member]
Off-balance sheet:
Contract amount, Off-balance sheet	12,763,000	8,330,000
Level 3 [Member] | Commitments [Member]
Off-balance sheet:
Contract amount, Off-balance sheet	767,274,000	705,316,000
Fair Value [Member] | Level 3 [Member]
Financial assets:
Loans, net	2,763,473,000	2,555,297,000
Financial liabilities:
Junior subordinated debt	49,033,000	44,527,000
Fair Value [Member] | Level 3 [Member] | Overdraft Privilege Commitments [Member]
Off-balance sheet:
Fair value, Off-balance sheet	986,000	945,000
Fair Value [Member] | Level 3 [Member] | Standby Letters of Credit [Member]
Off-balance sheet:
Fair value, Off-balance sheet	128,000	83,000
Fair Value [Member] | Level 3 [Member] | Commitments [Member]
Off-balance sheet:
Fair value, Off-balance sheet	7,673,000	7,053,000
Fair Value [Member] | Level 1 [Member]
Financial assets:
Cash and due from banks	92,197,000	94,305,000
Cash at Federal Reserve and other banks	213,415,000	209,156,000
Fair Value [Member] | Level 2 [Member]
Financial assets:
Securities held to maturity	603,203,000	732,208,000
Loans held for sale	2,998,000	1,873,000
Financial liabilities:
Deposits	3,893,941,000	3,630,129,000
Other borrowings	17,493,000	12,328,000
Carrying Amount [Member] | Level 3 [Member]
Financial assets:
Loans, net	2,727,090,000	2,486,926,000
Financial liabilities:
Junior subordinated debt	56,667,000	56,470,000
Carrying Amount [Member] | Level 1 [Member]
Financial assets:
Cash and due from banks	92,197,000	94,305,000
Cash at Federal Reserve and other banks	213,415,000	209,156,000
Carrying Amount [Member] | Level 2 [Member]
Financial assets:
Securities held to maturity	602,536,000	726,530,000
Restricted equity securities	16,956,000	16,596,000
Loans held for sale	2,998,000	1,873,000
Financial liabilities:
Deposits	3,895,560,000	3,631,266,000
Other borrowings	$ 17,493,000	$ 12,328,000