Loans - Contractual Aging of Recorded Investment in Past Due Loans by Portfolio Classification of Loans (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-59 Days Past Due	$ 451	$ 841
60-89 Days Past Due	583	270
Greater Than 90 Days	1,585	1,174
Total Past Due	2,619	2,285
Current	612,090	619,641
Total Financing Receivables	614,709	621,926	582,872
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	368	713
60-89 Days Past Due	580	50
Greater Than 90 Days	227	436
Total Past Due	1,175	1,199
Current	95,844	96,351
Total Financing Receivables	97,019	97,550	91,368
Recorded Investment > 90 Days and Accruing	0	0
Agricultural Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Greater Than 90 Days	222
Total Past Due	222
Current	51,174	50,895
Total Financing Receivables	51,396	50,895	49,629
Recorded Investment > 90 Days and Accruing	0	0
Agricultural [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-59 Days Past Due		25
Greater Than 90 Days	54
Total Past Due	54	25
Current	71,517	74,586
Total Financing Receivables	71,571	74,611	64,859
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	14	78
60-89 Days Past Due		204
Greater Than 90 Days	978	709
Total Past Due	992	991
Current	270,209	269,197
Total Financing Receivables	271,201	270,188	261,634
Recorded Investment > 90 Days and Accruing	0	0
Commercial and Industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-59 Days Past Due	35
60-89 Days Past Due		8
Greater Than 90 Days	84
Total Past Due	119	8
Current	99,776	104,816
Total Financing Receivables	99,895	104,824	94,358
Recorded Investment > 90 Days and Accruing	0	0
Consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-59 Days Past Due	34	25
60-89 Days Past Due	3	8
Greater Than 90 Days	20	29
Total Past Due	57	62
Current	23,570	23,796
Total Financing Receivables	23,627	23,858	21,024
Recorded Investment > 90 Days and Accruing	$ 0	$ 0

Financing receivables current and past due.

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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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- 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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