Allowance for Loan Losses - Loans by Risk Rating (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2012
Loans by risk rating
Financing Receivable, Net	$ 1,231,048	$ 1,111,788	$ 1,064,923
Construction and Land Development [Member]
Loans by risk rating
Financing Receivable, Net	32,750	38,618	38,318
Construction and Land Development [Member] | 1-3 (Pass) [Member]
Loans by risk rating
Financing Receivable, Net	23,789	29,719
Construction and Land Development [Member] | 4 (Monitor) [Member]
Loans by risk rating
Financing Receivable, Net	7,461	7,399
Construction and Land Development [Member] | 5 (Substandard) [Member]
Loans by risk rating
Financing Receivable, Net
Construction and Land Development [Member] | 6 (Doubtful) [Member]
Loans by risk rating
Financing Receivable, Net
Construction and Land Development [Member] | Impaired [Member]
Loans by risk rating
Financing Receivable, Net	1,500	1,500
Commercial and Industrial [Member]
Loans by risk rating
Financing Receivable, Net	87,468	88,475	78,567
Commercial and Industrial [Member] | 1-3 (Pass) [Member]
Loans by risk rating
Financing Receivable, Net	85,797	86,587
Commercial and Industrial [Member] | 4 (Monitor) [Member]
Loans by risk rating
Financing Receivable, Net	539	606
Commercial and Industrial [Member] | 5 (Substandard) [Member]
Loans by risk rating
Financing Receivable, Net
Commercial and Industrial [Member] | 6 (Doubtful) [Member]
Loans by risk rating
Financing Receivable, Net
Commercial and Industrial [Member] | Impaired [Member]
Loans by risk rating
Financing Receivable, Net	1,132	1,282
Commercial Real Estate [Member]
Loans by risk rating
Financing Receivable, Net	666,166	576,465	562,252
Commercial Real Estate [Member] | 1-3 (Pass) [Member]
Loans by risk rating
Financing Receivable, Net	660,114	569,760
Commercial Real Estate [Member] | 4 (Monitor) [Member]
Loans by risk rating
Financing Receivable, Net	1,364	4,424
Commercial Real Estate [Member] | 5 (Substandard) [Member]
Loans by risk rating
Financing Receivable, Net
Commercial Real Estate [Member] | 6 (Doubtful) [Member]
Loans by risk rating
Financing Receivable, Net
Commercial Real Estate [Member] | Impaired [Member]
Loans by risk rating
Financing Receivable, Net	$ 4,688	$ 2,281