Fair Value - Carrying Amount and Fair Value of Financial Instruments (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2013	Dec. 31, 2012
ASSETS
Cash and cash equivalents	$ 29,397	$ 29,633	$ 32,856	$ 31,881
Interest bearing time deposits with other banks	225	275
Securities available for sale	699,366	685,991
Trading securities	4,440	4,127
Loans held for sale	1,290	487
Net loans	1,308,532	1,279,129
FHLB and other equity interests	8,491	7,533
LIABILITIES
Deposits	(1,866,864)	(1,835,314)
Subordinated debentures	(20,620)	(20,620)
Carrying Amount [Member]
ASSETS
Cash and cash equivalents	29,397	29,633
Interest bearing time deposits with other banks	225	275
Securities available for sale	699,366	685,991
Trading securities	4,440	4,127
Loans held for sale	1,290	487
Net loans	1,308,532	1,279,129
FHLB and other equity interests	8,491	7,533
Accrued interest receivable	7,842	8,032
LIABILITIES
Deposits	(1,866,864)	(1,835,314)
FHLB and other borrowings	(83,877)	(87,950)
Subordinated debentures	(20,620)	(20,620)
Interest rate swaps	(936)	(1,116)
Accrued interest payable	(799)	(868)
Total Fair Value [Member]
ASSETS
Cash and cash equivalents	29,397	29,633
Interest bearing time deposits with other banks	224	274
Securities available for sale	699,366	685,991
Trading securities	4,440	4,127
Loans held for sale	1,290	507
Net loans	1,305,396	1,276,622
Accrued interest receivable	7,842	8,032
LIABILITIES
Deposits	(1,865,889)	(1,834,789)
FHLB and other borrowings	(83,846)	(87,833)
Subordinated debentures	(11,227)	(11,178)
Interest rate swaps	(936)	(1,116)
Accrued interest payable	(799)	(868)
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
ASSETS
Cash and cash equivalents	29,397	29,633
Interest bearing time deposits with other banks	0	0
Securities available for sale	997	985
Trading securities	4,182	3,923
Loans held for sale	0	0
Net loans	0	0
Accrued interest receivable	6	368
LIABILITIES
Deposits	(1,681,430)	(1,569,552)
FHLB and other borrowings	0	0
Subordinated debentures	0	0
Interest rate swaps	0	0
Accrued interest payable	(341)	(200)
Significant Other Observable Inputs (Level 2) [Member]
ASSETS
Cash and cash equivalents	0	0
Interest bearing time deposits with other banks	224	274
Securities available for sale	697,498	684,345
Trading securities	258	204
Loans held for sale	1,290	507
Net loans	0	0
Accrued interest receivable	4,072	3,302
LIABILITIES
Deposits	(184,459)	(265,237)
FHLB and other borrowings	(83,846)	(87,833)
Subordinated debentures	(11,227)	(11,178)
Interest rate swaps	(936)	(1,116)
Accrued interest payable	(443)	(653)
Significant Unobservable Inputs (Level 3) [Member]
ASSETS
Cash and cash equivalents	0	0
Interest bearing time deposits with other banks	0	0
Securities available for sale	871	661
Trading securities	0	0
Loans held for sale	0	0
Net loans	1,305,396	1,276,622
Accrued interest receivable	3,764	4,362
LIABILITIES
Deposits	0	0
FHLB and other borrowings	0	0
Subordinated debentures	0	0
Interest rate swaps	0	0
Accrued interest payable	$ (15)	$ (15)