Note 8 - Goodwill and Intangible Assets (Details) - Acquired Intangible Assets (Core Deposits [Member], USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Core Deposits [Member]
Core deposit intangibles resulting from bank and branch acquisitions:
Gross Amount	$ 7,930	$ 7,930	$ 7,930
Accumulated Amortization	(7,334)	(6,965)	(6,482)
Net Carrying Value	$ 596	$ 965	$ 1,448

Name:	fbmi_CoreDepositIntangiblesResultingFromBankAndBranchAcquisitionsAbstract
Namespace Prefix:	fbmi_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Accumulated amount of amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 350

-SubTopic 30

-Section 50

-Paragraph 2

-Subparagraph (a)(1)

-URI http://asc.fasb.org/extlink&oid=26713463&loc=d3e16323-109275

+ Details

Name:	us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount before amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life.

+ References

+ Details

Name:	us-gaap_FiniteLivedIntangibleAssetsGross
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount after amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life.

+ References

+ Details

Name:	us-gaap_FiniteLivedIntangibleAssetsNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant