Fair Value - Carrying Amount and Fair Value of Financial Instruments (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2012	Dec. 31, 2011	Jun. 30, 2013 Carrying Amount [Member]	Jan. 31, 2012 Carrying Amount [Member]	Jun. 30, 2013 Total Fair Value [Member]	Dec. 31, 2012 Total Fair Value [Member]	Jun. 30, 2013 Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]	Dec. 31, 2012 Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]	Jun. 30, 2013 Significant Other Observable Inputs (Level 2) [Member]	Dec. 31, 2012 Significant Other Observable Inputs (Level 2) [Member]	Jun. 30, 2013 Significant Unobservable Inputs (Level 3) [Member]	Dec. 31, 2012 Significant Unobservable Inputs (Level 3) [Member]
ASSETS
Cash and cash equivalents	$ 24,794	$ 31,881	$ 24,228	$ 39,703	$ 24,974	$ 31,881	$ 24,794	$ 31,881	$ 24,794	$ 31,881	$ 0	$ 0	$ 0	$ 0
Interest bearing time deposits with other banks	277	225			277	225	283	230	0	0	283	230	0	0
Securities available for sale	724,298	737,311			724,298	737,311	724,298	737,311	74,661	54,169	649,007	680,562	630	2,580
Trading securities	4,729	4,459			4,729	4,459	4,729	4,459	4,574	4,300	155	159	0	0
Loans held for sale	53	2,398			53	2,398	54	2,460	0	0	54	2,460	0	0
Net loans	967,447	913,764			967,447	913,764	949,183	917,785	0	0	0	0	949,183	917,785
FHLB and other equity interests	7,565	6,684			7,565	6,684
Accrued interest receivable					7,082	6,863	7,082	6,863	402	278	3,493	3,498	3,187	3,087
LIABILITIES
Deposits	(1,546,546)	(1,485,003)			(1,546,546)	(1,485,003)	(1,546,413)	(1,487,545)	(1,347,442)	(1,272,060)	(198,971)	(215,485)	0	0
FHLB and other borrowings					(100,477)	(97,806)	(99,872)	(105,850)	0	0	(99,872)	(105,850)	0	0
Subordinated debentures	(20,620)	(20,620)			(20,620)	(20,620)	(10,998)	(10,682)	0	0	(10,998)	(10,682)	0	0
Interest rate swaps					(1,253)	(1,745)	(1,253)	(1,745)	0	0	(1,253)	(1,745)	0	0
Accrued interest payable					$ (882)	$ (1,022)	$ (882)	$ (1,022)	$ (223)	$ (301)	$ (645)	$ (707)	$ (14)	$ (14)