Loans - Impaired Loans Classified as Troubled Debt Restructured (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
Mar. 31, 2015 Contract	Mar. 31, 2014 Contract
Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts Modified in the Last 3 Months	1
Pre-Modification Outstanding Recorded Investment	$ 528
Post-Modification Outstanding Recorded Investment	430
Agricultural Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts Modified in the Last 3 Months		2
Pre-Modification Outstanding Recorded Investment		153
Post-Modification Outstanding Recorded Investment		141
Commercial and Industrial [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts Modified in the Last 3 Months	1
Pre-Modification Outstanding Recorded Investment	28
Post-Modification Outstanding Recorded Investment	$ 24

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Number of financing receivables that have been modified by troubled debt restructurings.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 33

-URI http://asc.fasb.org/extlink&oid=35738203&loc=SL6953676-111524

+ Details

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Post-modification amount of investment in financing receivables modified by troubled debt restructurings.

+ References

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- Definition

Pre-modification amount of investment in financing receivables modified by troubled debt restructurings.

+ References

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