Business Combination Recognized Identifiable Assets Acquired.

Name:	fmer_BusinessCombinationRecognizedIdentifiableAssetsAcquired
Namespace Prefix:	fmer
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed.

+ Details

Name:	fmer_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumed
Namespace Prefix:	fmer
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Accrued Expenses And Other Liabilities.

+ Details

Name:	fmer_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAccruedExpensesAndOtherLiabilities
Namespace Prefix:	fmer
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Accrued Interest.

+ Details

Name:	fmer_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAccruedInterest
Namespace Prefix:	fmer
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Allowances For Loan Losses.

+ Details

Name:	fmer_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAllowancesForLoanLosses
Namespace Prefix:	fmer
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Cash And Due From Banks.

+ Details

Name:	fmer_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCashAndDueFromBanks
Namespace Prefix:	fmer
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Covered Commercial Loan.

+ Details

Name:	fmer_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCoveredCommercialLoan
Namespace Prefix:	fmer
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Covered Consumer Loan.

+ Details

Name:	fmer_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCoveredConsumerLoan
Namespace Prefix:	fmer
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Covered Installment Loan.

+ Details

Name:	fmer_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCoveredInstallmentLoan
Namespace Prefix:	fmer
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Business combination recognized identifiable assets acquired and liabilities assumed covered loan fair value.

+ Details

Name:	fmer_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCoveredLoanFairValue
Namespace Prefix:	fmer
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Covered Loans And Loss Share Receivable.

+ Details

Name:	fmer_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCoveredLoansAndLossShareReceivable
Namespace Prefix:	fmer
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Covered Loss share receivable other real estate.

+ Details

Name:	fmer_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCoveredLossShareReceivableOtherRealEstate
Namespace Prefix:	fmer
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Covered Mortgage Loan.

+ Details

Name:	fmer_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCoveredMortgageLoan
Namespace Prefix:	fmer
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Covered Other Real Estate.

+ Details

Name:	fmer_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCoveredOtherRealEstate
Namespace Prefix:	fmer
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Deposits.

+ Details

Name:	fmer_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeposits
Namespace Prefix:	fmer
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Fdic Liability.

+ Details

Name:	fmer_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedFdicLiability
Namespace Prefix:	fmer
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Investment Securities.

+ Details

Name:	fmer_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedInvestmentSecurities
Namespace Prefix:	fmer
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Loans.

+ Details

Name:	fmer_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLoans
Namespace Prefix:	fmer
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Non Interest Bearing Deposit Accounts.

+ Details

Name:	fmer_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNonInterestBearingDepositAccounts
Namespace Prefix:	fmer
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Other Assets.

+ Details

Name:	fmer_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherAssets
Namespace Prefix:	fmer
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Savings Deposits.

+ Details

Name:	fmer_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedSavingsDeposits
Namespace Prefix:	fmer
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Time Deposits.

+ Details

Name:	fmer_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedTimeDeposits
Namespace Prefix:	fmer
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Business Combination Recognized Identifiable Liabilities Assumed.

+ Details

Name:	fmer_BusinessCombinationRecognizedIdentifiableLiabilitiesAssumed
Namespace Prefix:	fmer
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Covered loans.

+ Details

Name:	fmer_CoveredLoansAbstract
Namespace Prefix:	fmer
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Expected reimbursement for losses incurred on covered loans.

+ Details

Name:	fmer_ExpectedReimbursementForLossesIncurredOnCoveredLoans
Namespace Prefix:	fmer
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	us-gaap_AssetsAbstract
Namespace Prefix:	us-gaap
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The amount of identifiable intangible assets recognized as of the acquisition date.

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

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 141R
-Paragraph 12, 13, 14, 20, A107
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 141R
-Paragraph 68
-Subparagraph i
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 10
-Section 55
-Paragraph 37
-URI http://asc.fasb.org/extlink&oid=6910123&loc=d3e2207-128464

+ Details

Name:	us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The amount of property, plant, and equipment recognized as of the acquisition date.

+ References

+ Details

Name:	us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	us-gaap_DepositsAbstract
Namespace Prefix:	us-gaap
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Carrying amount as of the balance sheet date, which is the cumulative amount paid and (if applicable) the fair value of any noncontrolling interest in the acquiree, adjusted for any amortization recognized prior to the adoption of any changes in generally accepted accounting principles (as applicable) and for any impairment charges, in excess of the fair value of net assets acquired in one or more business combination transactions.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 142
-Paragraph 45
-Subparagraph e
-Clause 1
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 142
-Paragraph 43
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 141R
-Paragraph 68
-Subparagraph l
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 142
-Paragraph 45
-Subparagraph e
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 141R
-Paragraph 34
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 6: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6905597&loc=d3e13816-109267

Reference 7: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6388280&loc=d3e13770-109266

Reference 8: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 141R
-Paragraph 72
-Subparagraph d
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

+ Details

Name:	us-gaap_Goodwill
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Business Combination (Details) (USD $) In Thousands	Jun. 30, 2011	Dec. 31, 2010	Jun. 30, 2010	Feb. 19, 2010 Acquired Book Value [Member] First Bank Branches [Member]	Jun. 30, 2011 Acquired Book Value [Member] Midwest Bank and Trust Company [Member]	Feb. 19, 2010 Fair Value Adjustments [Member] First Bank Branches [Member]	Jun. 30, 2011 Fair Value Adjustments [Member] Midwest Bank and Trust Company [Member]	Jun. 30, 2011 Fair Value Adjustments [Member] George Washington Savings Bank [Member]	Feb. 19, 2010 As Recorded by FirstMerit Bank, N.A. [Member] First Bank Branches [Member]	Jun. 30, 2011 As Recorded by FirstMerit Bank, N.A. [Member] Midwest Bank and Trust Company [Member]	Jun. 30, 2011 As Recorded by FirstMerit Bank, N.A. [Member] George Washington Savings Bank [Member]	Jun. 30, 2011 Recorded By FDIC Member Midwest Bank and Trust Company [Member]	Jun. 30, 2011 Recorded By FDIC Member George Washington Savings Bank [Member]	Jun. 30, 2011 Midwest Bank and Trust Company [Member]	May 14, 2010 Midwest Bank and Trust Company [Member]	Jun. 30, 2011 George Washington Savings Bank [Member]	Feb. 19, 2010 George Washington Savings Bank [Member]
ASSETS
Cash and due from banks				$ 3,725		$ 0	$ 0	$ 0	$ 3,725	$ 279,352	$ 57,984	$ 279,352	$ 57,984
Investment securities							(977)	0		564,233	15,410	565,210	15,410
Loans				301,236		(25,624)			275,612
Covered loans
Commercial loan							(317,526)	(117,879)		1,522,475	136,613	1,840,001	254,492
Consumer loans							(53,742)			258,389		312,131
Mortgage Loan								(2,860)			24,358		27,218
Installment loan								(7,298)			16,780		24,078
Total covered loans							(371,268)	(128,037)		1,780,864	177,751	2,152,132	305,788		1,800,000		177,800
Allowance for loan losses							5,465			0		(5,465)
Accrued interest							(5,436)			0		5,436
Loss share receivable							260,730	88,694		260,730	88,694	0	0	260,700		88,700
Total covered loans and loss share receivable							(110,509)	(39,343)		2,041,594	266,445	2,152,103	305,788
Core deposit intangible				0		3,154	7,433	962	3,154	7,433	962	0	0
Covered other real estate							(1,165)	(7,561)		26,155	11,460	27,320	19,021
Loss share receivable-other real estate							2,196	11,339		2,196	11,339	0	0
Premises and equipment				22,992		18,963			41,955
Goodwill	460,044	460,044	460,045	0	272,100	48,347	272,099		48,347	272,099		0		2,200
Other assets				941		3,115	19,054	0	4,056	28,892	5,680	9,838	5,680
Total assets acquired				328,894		47,955	188,131	(34,603)	376,849	3,221,954	369,280	3,033,823	403,883
Deposits:
Non Interest Bearing Deposit Accounts								0			54,242		54,242
Savings deposits							0	0		748,681	62,737	748,681	62,737
Time deposits							9,125	4,921		1,509,038	283,676	1,499,913	278,755
Deposits				1,199,279		7,134	9,125	4,921	1,206,413	2,257,719	400,655	2,248,594	395,734
Borrowings							83,241			723,045		639,804
FDIC Liability							6,256			6,256		0
Accrued expenses and other liabilities				4,192		(1,271)	0	5,191	2,921	7,395	7,760	7,395	2,569
Total liabilities assumed				$ 1,203,471		$ 5,863	$ 98,622	$ 10,112	$ 1,209,334	$ 2,994,415	$ 408,415	$ 2,895,793	$ 398,303