Allowance for Loan Losses - Loans by Risk Rating (Detail) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015	Jun. 30, 2015
Loans by risk rating
Financing Receivable, Net	$ 1,801,904	$ 1,731,536	$ 1,544,694
Construction and Land Development [Member]
Loans by risk rating
Financing Receivable, Net	31,178	27,421	26,521
Construction and Land Development [Member] | 1-3 (Pass) [Member]
Loans by risk rating
Financing Receivable, Net	24,048	20,281
Construction and Land Development [Member] | 4 (Monitor) [Member]
Loans by risk rating
Financing Receivable, Net	7,034	7,042
Construction and Land Development [Member] | Impaired [Member]
Loans by risk rating
Financing Receivable, Net	96	98
Commercial and Industrial [Member]
Loans by risk rating
Financing Receivable, Net	493,033	452,235	291,142
Commercial and Industrial [Member] | 1-3 (Pass) [Member]
Loans by risk rating
Financing Receivable, Net	492,623	451,774
Commercial and Industrial [Member] | 4 (Monitor) [Member]
Loans by risk rating
Financing Receivable, Net		18
Commercial and Industrial [Member] | Impaired [Member]
Loans by risk rating
Financing Receivable, Net	410	443
Municipal [Member]
Loans by risk rating
Financing Receivable, Net	134,386	85,685	87,241
Municipal [Member] | 1-3 (Pass) [Member]
Loans by risk rating
Financing Receivable, Net	134,386	85,685
Commercial Real Estate [Member]
Loans by risk rating
Financing Receivable, Net	728,658	721,506	$ 713,770
Commercial Real Estate [Member] | 1-3 (Pass) [Member]
Loans by risk rating
Financing Receivable, Net	724,735	718,911
Commercial Real Estate [Member] | 4 (Monitor) [Member]
Loans by risk rating
Financing Receivable, Net	187	917
Commercial Real Estate [Member] | Impaired [Member]
Loans by risk rating
Financing Receivable, Net	$ 3,736	$ 1,678