Business Combinations (Tables)

12 Months Ended

Dec. 31, 2011

First Bank Branches [Member]

Business Acquisition [Line Items]

Schedule of Recognized Identified Assets Acquired and Liabilities Assumed [Table Text Block]

	Acquired Book Value		Fair Value Adjustments			As Recorded by FirstMerit Bank, N.A.
Assets
Cash and due from banks	$	3,725	$	—		$	3,725
Loans	301,236		(25,624		)	275,612
Premises and equipment	22,992		18,963			41,955
Goodwill	—		48,347			48,347
Core deposit intangible	—		3,154			3,154
Other assets	941		3,115			4,056
Total assets acquired	$	328,894	$	47,955		$	376,849
Liabilities
Deposits	$	1,199,279	$	7,134		$	1,206,413
Accrued expenses and other liabilities	4,192		(1,271		)	2,921
Total liabilities assumed	$	1,203,471	$	5,863		$	1,209,334

George Washington Savings Bank [Member]

Business Acquisition [Line Items]

Schedule of Recognized Identified Assets Acquired and Liabilities Assumed [Table Text Block]

				As Recorded by FDIC		Fair Value Adjustments			As Recorded by FirstMerit Bank, N.A.
Assets
	Cash and due from banks			$	57,984	$	—		$	57,984
	Investment securities			15,410		—			15,410
	Covered loans
		Commercial loan		254,492		(117,879		)	136,613
		Mortgage loan		27,218		(2,860		)	24,358
		Installment loan		24,078		(7,298		)	16,780
			Total covered loans	305,788		(128,037		)	177,751
		Loss share receivable - loans		—		88,694			88,694
			Total covered loans and loss share receivable	305,788		(39,343		)	266,445
	Core deposit intangible			—		962			962
	Covered other real estate			19,021		(7,561		)	11,460
		Loss share receivable - other real estate		—		11,339			11,339
	Other assets			5,680		—			5,680
		Total assets acquired		$	403,883	$	(34,603	)	$	369,280
Liabilities
	Deposits
		Noninterest-bearing deposit accounts		$	54,242	$	—		$	54,242
		Savings deposits		62,737		—			62,737
		Time deposits		278,755		4,921			283,676
		Total deposits		395,734		4,921			400,655
	Accrued expenses and other liabilities			2,569		5,191			7,760
		Total liabilities assumed		$	398,303	$	10,112		$	408,415

Midwest Bank and Trust Company [Member]

Business Acquisition [Line Items]

Estimated fair values of the assets acquired and liabilities assumed at the date of acquisition

				As Recorded by FDIC			Fair Value Adjustments			As Recorded by FirstMerit Bank, N.A.
Assets
	Cash and due from banks			$	279,352		$	—		$	279,352
	Investment securities			565,210			(977		)	564,233
		Commercial loans		1,840,001			(317,526		)	1,522,475
		Consumer loans		312,131			(53,742		)	258,389
			Total covered loans	2,152,132			(371,268		)	1,780,864
		Allowance for loan losses		(5,465		)	5,465			—
		Accrued interest		5,436			(5,436		)	—
		Loss share receivable - loans		—			260,730			260,730
			Total covered loans and loss share receivable	2,152,103			(110,509		)	2,041,594
	Core deposit intangible			—			7,433			7,433
	Covered other real estate			27,320			(1,165		)	26,155
		Loss share receivable - other real estate		—			2,196			2,196
	Goodwill			—			272,099			272,099
	Other assets			9,838			19,054			28,892
		Total assets acquired		$	3,033,823		$	188,131		$	3,221,954
Liabilities
	Deposits
		Savings deposits		$	748,681		$	—		$	748,681
		Time deposits		1,499,913			9,125			1,509,038
		Total deposits		2,248,594			9,125			2,257,719
	Borrowings			639,804			83,241			723,045
	FDIC liability			—			6,256			6,256
	Accrued expenses and other liabilities			7,395			—			7,395
		Total liabilities assumed		$	2,895,793		$	98,622		$	2,994,415