Benefit Plans Schedule of Net Benefit Costs Details (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
FirstMerit | Pension and post- retirement costs
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Service Cost	$ 585	$ 1,799	$ 1,755	$ 5,397
Defined Benefit Plan, Interest Cost	2,632	2,965	7,896	8,895
Defined Benefit Plan, Expected Return on Plan Assets	(2,960)	(3,034)	(8,880)	(9,102)
Defined Benefit Plan, Amortization of Prior Service Cost (Credit)	117	97	351	291
Defined Benefit Plan, Amortization of Gains (Losses)	1,174	2,593	3,522	7,779
Defined Benefit Plan, Net Periodic Benefit Cost	1,548	4,420	4,644	13,260
FirstMerit | Other Postretirement Benefit Plans, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Service Cost	24	19	74	57
Defined Benefit Plan, Interest Cost	130	174	390	522
Defined Benefit Plan, Amortization of Prior Service Cost (Credit)	(117)	(117)	(351)	(351)
Defined Benefit Plan, Amortization of Gains (Losses)	67	72	201	216
Defined Benefit Plan, Net Periodic Benefit Cost	104	148	314	444
Citizens Republic Bancorp | Pension and post- retirement costs
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Interest Cost	795		1,590
Defined Benefit Plan, Expected Return on Plan Assets	(1,096)		(2,192)
Defined Benefit Plan, Net Periodic Benefit Cost	(301)		(602)
Citizens Republic Bancorp | Other Postretirement Benefit Plans, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Interest Cost	15,770		31,540
Defined Benefit Plan, Net Periodic Benefit Cost	$ 15,770		$ 31,540