Summary of Activity in Allowances for Loan Losses (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended	12 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Dec. 31, 2011
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period			$ 4,932	$ 3,447
Provision			2,586	2,302
Charge-offs	(100)	(100)	(1,406)	(853)
Recoveries			46	36
Balance at end of period	6,158		6,158	4,932
Individually Evaluated for Impairment	2,983		2,983	2,156
Collectively Evaluated for Impairment	3,175		3,175	2,776
Loan Ending Balance:	462,544		462,544	420,636
Individually Evaluated for Impairment	21,705		21,705	23,317
Collectively Evaluated for Impairment	440,839		440,839	397,319
Commercial and Industrial
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period			899	825
Provision			773	211
Charge-offs			(200)	(148)
Recoveries			11	11
Balance at end of period	1,483		1,483	899
Individually Evaluated for Impairment	926		926	407
Collectively Evaluated for Impairment	557		557	492
Loan Ending Balance:	93,893		93,893	94,876
Individually Evaluated for Impairment	5,291		5,291	5,123
Collectively Evaluated for Impairment	88,602		88,602	89,753
Construction & Development
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period			1,048	785
Provision			450	563
Charge-offs			(508)	(300)
Balance at end of period	990		990	1,048
Individually Evaluated for Impairment	225		225	529
Collectively Evaluated for Impairment	765		765	519
Loan Ending Balance:	66,709		66,709	51,078
Individually Evaluated for Impairment	672		672	2,391
Collectively Evaluated for Impairment	66,037		66,037	48,687
Commercial Real Estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period			2,313	1,049
Provision			1,323	1,460
Charge-offs			(693)	(196)
Recoveries			17
Balance at end of period	2,960		2,960	2,313
Individually Evaluated for Impairment	1,400		1,400	1,078
Collectively Evaluated for Impairment	1,560		1,560	1,235
Loan Ending Balance:	250,160		250,160	231,819
Individually Evaluated for Impairment	14,000		14,000	15,661
Collectively Evaluated for Impairment	236,160		236,160	216,158
Residential Real Estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period			633	753
Provision			64	57
Charge-offs				(202)
Recoveries			18	25
Balance at end of period	715		715	633
Individually Evaluated for Impairment	432		432	142
Collectively Evaluated for Impairment	283		283	491
Loan Ending Balance:	49,841		49,841	40,826
Individually Evaluated for Impairment	1,723		1,723	142
Collectively Evaluated for Impairment	48,118		48,118	40,684
Consumer Loan
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period			39	35
Provision			(24)	11
Charge-offs			(5)	(7)
Balance at end of period	10		10	39
Collectively Evaluated for Impairment	10		10	39
Loan Ending Balance:	1,941		1,941	2,037
Individually Evaluated for Impairment	19		19
Collectively Evaluated for Impairment	$ 1,922		$ 1,922	$ 2,037