Impaired Loans (Detail) (USD $) In Thousands, unless otherwise specified	6 Months Ended	12 Months Ended
	Jun. 30, 2012	Dec. 31, 2011
Financing Receivable, Impaired [Line Items]
Loans receivable for which there is a related allowance for credit losses determined in accordance with ASC 310-10/Statement No. 114	$ 1,636	$ 1,923
Unpaid Principal Balance	33,337	34,452
Other impaired loans	26,751	25,550
Total impaired loans, Recorded Investment	28,387	27,473
Average monthly balance of impaired loans	32,602	29,916
Related Allowance	692	439
Average Recorded Investment	30,862	30,963
Commercial
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance	24,404	26,676
Total impaired loans, Recorded Investment	20,523	20,708
Related Allowance	619	366
Average Recorded Investment	22,463	23,692
Consumer
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance	6,913	5,885
Total impaired loans, Recorded Investment	5,915	4,933
Related Allowance	73	73
Average Recorded Investment	6,415	5,409
Owner Occupied Residential Real Estate Loans
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance	2,020	1,891
Total impaired loans, Recorded Investment	1,949	1,832
Average Recorded Investment	1,984	1,862
Impaired Financing Receivables with No Related Allowance | Commercial Real Estate
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance	20,113	22,454
Total impaired loans, Recorded Investment	16,712	16,949
Average Recorded Investment	18,412	19,702
Impaired Financing Receivables with No Related Allowance | Commercial Non Real Estate
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance	2,727	2,376
Total impaired loans, Recorded Investment	2,408	2,075
Average Recorded Investment	2,568	2,225
Impaired Financing Receivables with No Related Allowance | Other Consumer
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance	6,163	5,135
Total impaired loans, Recorded Investment	5,192	4,203
Average Recorded Investment	5,678	4,669
Impaired Financing Receivables with No Related Allowance | Consumer Home Equity
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance	517	511
Total impaired loans, Recorded Investment	490	491
Average Recorded Investment	504	501
Impaired Financing Receivables with No Related Allowance | Residential 1-4 family
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance	2,020
Total impaired loans, Recorded Investment	1,949
Average Recorded Investment	1,984
Impaired Financing Receivables with No Related Allowance | Residential Real Estate | Residential 1-4 family
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance		1,891
Total impaired loans, Recorded Investment		1,832
Average Recorded Investment		1,862
Impaired Financing Receivables with Related Allowance | Commercial Real Estate
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance	1,564	1,564
Total impaired loans, Recorded Investment	1,403	1,403
Related Allowance	619	306
Average Recorded Investment	1,483	1,483
Impaired Financing Receivables with Related Allowance | Commercial Non Real Estate
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance	233	282
Total impaired loans, Recorded Investment	233	281
Related Allowance	73	60
Average Recorded Investment	233	282
Impaired Financing Receivables with Related Allowance | Other Consumer
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance		239
Total impaired loans, Recorded Investment		239
Related Allowance		73
Average Recorded Investment		$ 239