Shareholders' Equity Earnings Per Share (Details) (USD $)	3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013 Stock Options [Member]	Jun. 30, 2012 Stock Options [Member]	Jun. 30, 2013 Stock Options [Member]	Jun. 30, 2012 Stock Options [Member]	Apr. 12, 2013 Citizens Republic Bancorp	Feb. 04, 2013 Citizens Republic Bancorp	Apr. 12, 2013 FirstMerit [Member] Citizens Republic Bancorp	Jun. 30, 2013 Series B Preferred Stock [Member]	Jun. 30, 2013 Series A Non-Cumulative Perpetual Preferred Stock [Member]	Feb. 04, 2013 Series A Non-Cumulative Perpetual Preferred Stock [Member]	Dec. 31, 2012 Series A Non-Cumulative Perpetual Preferred Stock [Member]	Jun. 30, 2012 Series A Non-Cumulative Perpetual Preferred Stock [Member]	Jun. 30, 2013 Series A Preferred Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Intrinsic Value	$ 3,900,000	$ 1,800,000	$ 3,900,000	$ 1,800,000
Business Acquisition, Equity Interest Issued or Issuable, Share Conversion Ratio									1.37
Stock issued for Citizens acquisition									55,468,283
Average common and common stock equivalent shares outstanding	157,982,000	109,562,000	133,969,000	109,386,000	119,000	0	60,000	0
Net income	48,450,000	30,585,000	85,796,000	60,929,000
Dividends, Preferred Stock	1,469,000	0	2,399,000	0
Undistributed Earnings Allocated to Participating Securities	384,000	113,000	813,000	143,000
Net income available to common shareholders	46,597,000	30,472,000	82,584,000	60,786,000
Average Common Shares Outstanding Prior to Participating Share Adjustment	159,158,000	110,598,000	135,204,000	110,422,000
Incremental Common Shares Attributable to Participating Nonvested Shares with Non-forfeitable Dividend Rights	1,295,000	1,036,000	1,295,000	1,036,000
Weighted average number of common shares outstanding - basic	157,863,000	109,562,000	133,909,000	109,386,000
Earnings Per Share, Basic	$ 0.30	$ 0.28	$ 0.62	$ 0.56
Income used in diluted earnings per share calculation	$ 46,597,000	$ 30,472,000	$ 82,584,000	$ 60,786,000
Weighted average number of shares outstanding prior to participating share adjustment	159,158,000	110,598,000	135,204,000	110,422,000
Earnings Per Share, Diluted	$ 0.29	$ 0.28	$ 0.62	$ 0.56
Class of Warrant or Right, Number of Securities Called by Warrants or Rights											2,408,203
Preferred Stock, Shares Authorized	7,000,000		7,000,000									220,000	115,000		0	0	800,000
Preferred Stock, Shares Outstanding													100,000	100,000	0	0
Interest rate of Non-Cumulative Perpetual Preferred Stock, Series A										5.875%