Loans - Contractual Aging of Recorded Investment in Past Due Loans by Portfolio Classification of Loans (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-59 Days Past Due	$ 841	$ 806
60-89 Days Past Due	270	2
Greater Than 90 Days	1,174	633
Total Past Due	2,285	1,441
Current	619,641	574,672
Total Financing Receivables	621,926	576,113
Recorded Investment > 90 Days and Accruing	0	0	0
Consumer Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-59 Days Past Due	713	778
60-89 Days Past Due	50	0
Greater Than 90 Days	436	234
Total Past Due	1,199	1,012
Current	96,351	91,426
Total Financing Receivables	97,550	92,438
Recorded Investment > 90 Days and Accruing	0	0
Agricultural Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	50,895	44,301
Total Financing Receivables	50,895	44,301
Recorded Investment > 90 Days and Accruing	0	0
Agricultural [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-59 Days Past Due	25
Total Past Due	25
Current	74,586	65,449
Total Financing Receivables	74,611	65,449
Recorded Investment > 90 Days and Accruing	0	0
Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-59 Days Past Due	78
60-89 Days Past Due	204
Greater Than 90 Days	709	373
Total Past Due	991	373
Current	269,197	248,520
Total Financing Receivables	270,188	248,893
Recorded Investment > 90 Days and Accruing	0	0
Commercial and Industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
60-89 Days Past Due	8
Greater Than 90 Days		26
Total Past Due	8	26
Current	104,816	103,830
Total Financing Receivables	104,824	103,856
Recorded Investment > 90 Days and Accruing	0	0
Consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-59 Days Past Due	25	28
60-89 Days Past Due	8	2
Greater Than 90 Days	29
Total Past Due	62	30
Current	23,796	21,146
Total Financing Receivables	23,858	21,176
Recorded Investment > 90 Days and Accruing	$ 0	$ 0

Financing receivables current and past due.

No definition available.

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- Definition

Financing receivables that are less than 60 days past due but more than 29 days past due.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 7A

-URI http://asc.fasb.org/extlink&oid=35738203&loc=SL6953401-111524

+ Details

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- Definition

Financing receivables that are less than 90 days past due but more than 59 days past due.

+ References

+ Details

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Period Type:	instant

- Definition

Recorded investment in financing receivables that are 90 days or more past due and still accruing.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 7

-Subparagraph (d)

-URI http://asc.fasb.org/extlink&oid=35738203&loc=d3e5111-111524

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- Definition

Financing receivables that are current.

+ References

+ Details

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- Definition

Financing receivables that are equal to or greater than 90 days past due.

+ References

+ Details

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- Definition

Recorded Investment in financing receivables that are past due at the balance sheet date.

+ References

+ Details

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