Allowance for Loan Losses by Portfolio Class (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended	9 Months Ended
Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Financing Receivable Allowance For Credit Losses [Line Items]
Beginning Balance	$ 15,692	$ 14,780	$ 15,312	$ 13,317
Provision for Loan Losses	640	1,300	1,721	3,900
Recoveries	107	157	256	343
Loans Charged-off	(517)	(1,071)	(1,367)	(2,394)
Ending Balance	15,922	15,166	15,922	15,166
Commercial and Industrial Loans and Leases [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Beginning Balance	4,707	4,292	3,493	3,713
Provision for Loan Losses	193	90	1,466	845
Recoveries	8	90	57	96
Loans Charged-off	(54)	(82)	(162)	(264)
Ending Balance	4,854	4,390	4,854	4,390
Commercial Real Estate Loans [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Beginning Balance	8,732	7,697	9,297	7,497
Provision for Loan Losses	376	1,120	232	2,007
Recoveries	62	28	88	131
Loans Charged-off	(351)	(714)	(798)	(1,504)
Ending Balance	8,819	8,131	8,819	8,131
Agricultural Loans [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Beginning Balance	890	733	926	750
Provision for Loan Losses	21	(5)	(15)	(22)
Recoveries	0	0	0	0
Loans Charged-off	0	0	0	0
Ending Balance	911	728	911	728
Home Equity Loans [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Beginning Balance	181	213	258	220
Provision for Loan Losses	21	108	(9)	194
Recoveries	0	2	1	5
Loans Charged-off	(7)	(29)	(55)	(125)
Ending Balance	195	294	195	294
Consumer Loans [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Beginning Balance	227	400	190	362
Provision for Loan Losses	12	54	141	138
Recoveries	35	37	99	96
Loans Charged-off	(63)	(85)	(219)	(190)
Ending Balance	211	406	211	406
Residential Mortgage Loans [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Beginning Balance	391	746	402	543
Provision for Loan Losses	(12)	57	59	395
Recoveries	2	0	11	15
Loans Charged-off	(42)	(161)	(133)	(311)
Ending Balance	339	642	339	642
Unallocated [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Beginning Balance	564	699	746	232
Provision for Loan Losses	29	(124)	(153)	343
Recoveries	0	0	0	0
Loans Charged-off	0	0	0	0
Ending Balance	$ 593	$ 575	$ 593	$ 575

Reflects a reduction in bad debt expense attributable to collections of loans and lease receivables which had previously been fully or partially charged off as bad debts.

+ References+ Details

Reflects the amount of loans and leases that have been removed, or charged off, from both loan receivables and the reserve for credit losses, typically because they are considered to be not salvageable or have been purchased by unconsolidated collection entities.

+ References+ Details

- Definition

Amount of allowance to cover probable credit losses on loans and leases. Includes carryover of or adjustments to the allowance for loan losses in connection with business combinations. Excludes allowance for loans and leases covered under loss sharing agreements.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 5

-Paragraph 8, 9

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 30

-Section 50

-Paragraph 2

-Subparagraph (b)(1)(ii)

-URI http://asc.fasb.org/extlink&oid=6379141&loc=d3e15032-111544

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-03.7(d))

-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher OTS

-Name Federal Regulation (FR)

-Number Title 12

-Section 563c.102

-Paragraph 8

-Subparagraph a(ii)

-Chapter V

-Subsection I

-LegacyDoc This is a non-GAAP reference that was included in the 2009 taxonomy. It will be removed from future versions of this taxonomy.

Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 7

-Subparagraph d

-Article 9

Reference 6: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 114

-Paragraph 20

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 7: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Staff Accounting Bulletin (SAB)

-Number Topic 6

-Section L

-Subsection 1

+ Details

- Definition

Provision charged for the period based on estimated losses to be realized from loan and lease transactions.

+ References+ Details