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Securities - Additional Information (Detail) (USD $)	12 Months Ended	3 Months Ended
	Dec. 31, 2014	Mar. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Investments with a carrying value and fair value		176,900,000us-gaap_PledgedFinancialInstrumentsNotSeparatelyReportedSecuritiesPledged
Increase decrease in investments with a carrying value and fair value	$ 8,000fmao_IncreaseDecreasePledgedFinancialInstrumentsNotSeparatelyReportedSecuritiesPledged
Minimum [Member]
Schedule of Available-for-sale Securities [Line Items]
Underwater security		10 years
Loss position existed		3 years

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- Definition

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+ References

No definition available.

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- Definition

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+ References

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- Definition

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+ References

No definition available.

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- Definition

Sum of the carrying amounts as of the date of the latest financial statement presented of securities which are owned but transferred to another party to serve as collateral to partially or fully secure a debt obligation, repurchase agreement or other current or potential obligation, and for which the transferee is not permitted to sell or re-pledge them to an unrelated party.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 860

-SubTopic 30

-Section 50

-Paragraph 1A

-Subparagraph (b)(1)(i)

-URI http://asc.fasb.org/extlink&oid=34720971&loc=SL6224234-111729

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