Business Combinations Non-impaired Cash Flows Reconciliation at Acquisition Date (Details) (Citizens Republic Bancorp, non-impaired, USD $) In Thousands, unless otherwise specified	Apr. 12, 2013
Citizens Republic Bancorp \| non-impaired
Nonimpaired Loans Cash Flows Reconciliation at Acquisition Date [Line Items]
Business Combination, Acquired Receivables, Gross Contractual Amount	$ 4,955,180
Business Combination, Acquired Receivables, Estimated Uncollectible	680,664
Contractually required payments at acquisition date, net of uncollectibles	$ 4,274,516

Contractually required payments at acquisition date, net of uncollectibles

No definition available.

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Namespace Prefix:	fmer_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	fmer_NonimpairedLoansCashFlowsReconciliationatAcquisitionDateLineItems
Namespace Prefix:	fmer_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

For receivables acquired in a business combination, excluding certain loans and debt securities acquired in a transfer (as defined), this element represents the best estimate at the acquisition date of the contractual cash flows not expected to be collected, by major class of receivable, such as loans, direct finance leases (as defined), and any other class of receivables.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 805

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (b)(3)

-URI http://asc.fasb.org/extlink&oid=6910749&loc=d3e4845-128472

+ Details

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

- Definition

For receivables acquired in a business combination, excluding certain loans and debt securities acquired in a transfer (as defined), this element represents the gross contractual amounts receivable, by major class of receivable, such as loans, direct finance leases (as defined), and any other class of receivables.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 805

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (b)(2)

-URI http://asc.fasb.org/extlink&oid=6910749&loc=d3e4845-128472

+ Details

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