Benefit Plans Schedule of Net Benefit Costs Details (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
FirstMerit [Member] | Pension and post- retirement costs
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Service Cost	$ 585	$ 1,799	$ 1,170	$ 3,598
Defined Benefit Plan, Interest Cost	2,632	2,965	5,264	5,930
Defined Benefit Plan, Expected Return on Plan Assets	(2,960)	(3,034)	(5,920)	(6,068)
Defined Benefit Plan, Amortization of Prior Service Cost (Credit)	117	97	234	194
Defined Benefit Plan, Amortization of Gains (Losses)	1,174	2,593	2,348	5,186
Defined Benefit Plan, Net Periodic Benefit Cost	1,548	4,420	3,096	8,840
FirstMerit [Member] | Other Postretirement Benefit Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Service Cost	25	19	50	38
Defined Benefit Plan, Interest Cost	130	174	260	348
Defined Benefit Plan, Amortization of Prior Service Cost (Credit)	(117)	(117)	(234)	(234)
Defined Benefit Plan, Amortization of Gains (Losses)	67	72	134	144
Defined Benefit Plan, Net Periodic Benefit Cost	105	148	210	296
Citizens Republic Bancorp | Pension and post- retirement costs
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Interest Cost	795
Defined Benefit Plan, Expected Return on Plan Assets	(1,096)
Defined Benefit Plan, Net Periodic Benefit Cost	(301)
Citizens Republic Bancorp | Other Postretirement Benefit Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Interest Cost	16
Defined Benefit Plan, Net Periodic Benefit Cost	$ 16