Loans - Allowance for Loan Losses Disaggregated on the Basis of Impairment Methodology (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Jun. 30, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Dec. 31, 2011
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans individually evaluated for impairment	$ 19,423		$ 17,537	$ 16,450
Loans collectively evaluated for impairment	73,724		86,916	88,951
Ending balance	93,147	93,400	104,453	105,401	105,648	110,147
Commercial and Industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans individually evaluated for impairment	15,912		13,171	14,301
Loans collectively evaluated for impairment	38,666		40,993	37,241
Ending balance	54,578	50,814	54,164	51,542	53,475	42,774
Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans individually evaluated for impairment	3,511		4,366	2,149
Loans collectively evaluated for impairment	18,205		24,980	25,492
Ending balance	21,716	23,573	29,346	27,641	27,631	20,912
Consumer Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans individually evaluated for impairment	0		0	0
Loans collectively evaluated for impairment	5,098		5,252	5,394
Ending balance	5,098	4,917	5,252	5,394	5,235	3,540
Consumer and Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans individually evaluated for impairment	0		0	0
Loans collectively evaluated for impairment	4,682		3,507	3,902
Ending balance	4,682	4,130	3,507	3,902	3,649	12,635
Unallocated [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans individually evaluated for impairment	0		0	0
Loans collectively evaluated for impairment	7,073		12,184	16,922
Ending balance	$ 7,073	$ 9,966	$ 12,184	$ 16,922	$ 15,658	$ 30,286