Name:	fmao_FinancingReceivableModificationsNumberOfContractsLineItems
Namespace Prefix:	fmao_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Financing Receivable Modifications Post Modification Recorded Investment One

+ References

No definition available.

+ Details

Name:	fmao_FinancingReceivableModificationsPostModificationRecordedInvestmentOne
Namespace Prefix:	fmao_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Financing Receivable Modifications Pre Modification Recorded Investment One

+ References

No definition available.

+ Details

Name:	fmao_FinancingReceivableModificationsPreModificationRecordedInvestmentOne
Namespace Prefix:	fmao_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

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=28368275&loc=SL6953676-111524

+ Details

Name:	us-gaap_FinancingReceivableModificationsNumberOfContracts2
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of financing receivables that have been modified by troubled debt restructurings within the previous 12 months and for which there was a payment default.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 34

-URI http://asc.fasb.org/extlink&oid=28368275&loc=SL6953682-111524

+ Details

Name:	us-gaap_FinancingReceivableModificationsSubsequentDefaultNumberOfContracts1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of investment related to financing receivables modified by troubled debt restructurings within the previous 12 months, for which there was a payment default.

+ References

+ Details

Name:	us-gaap_FinancingReceivableModificationsSubsequentDefaultRecordedInvestment1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

LOANS - Impaired Loans Classified as Troubled Debt Restructured (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013 Contract	Jun. 30, 2012 Contract	Jun. 30, 2013 Contract	Jun. 30, 2012 Contract
Commercial Real Estate [Member]
Financing Receivable Modifications Number Of Contracts [Line Items]
Number of Contracts Modified, Troubled Debt Restructurings That Subsequently Defaulted
Recorded Investment
Number of Contracts Modified, Troubled Debt Restructurings		1		1
Pre- Modification Outstanding Recorded Investment		1,937		1,937
Post- Modification Outstanding Recorded Investment		1,937		1,937
Agricultural Real Estate [Member]
Financing Receivable Modifications Number Of Contracts [Line Items]
Number of Contracts Modified, Troubled Debt Restructurings That Subsequently Defaulted
Recorded Investment
Number of Contracts Modified, Troubled Debt Restructurings
Pre- Modification Outstanding Recorded Investment
Post- Modification Outstanding Recorded Investment
Commercial and Industrial [Member]
Financing Receivable Modifications Number Of Contracts [Line Items]
Number of Contracts Modified, Troubled Debt Restructurings That Subsequently Defaulted
Recorded Investment
Number of Contracts Modified, Troubled Debt Restructurings	3		4
Pre- Modification Outstanding Recorded Investment	2,251		2,294
Post- Modification Outstanding Recorded Investment	$ 2,251		$ 2,332