Branch Sale (Details) (USD $)	9 Months Ended
	Sep. 30, 2012	Dec. 31, 2011	Sep. 30, 2012 Midland, Michigan [Member]	May 23, 2012 Midland, Michigan [Member]	May 23, 2012 Battle Creek, Michigan market area [Member]	May 23, 2012 Northeast Michigan [Member]
Branch Location [Line Items]
Number of branches to be sold				21	6	15
Loans [Abstract]
Commercial	$ 603,538,000	$ 651,155,000	$ 31,060,000
Mortgage	537,107,000	590,876,000	8,569,000
Installment	197,736,000	219,559,000	13,582,000
Total loans	1,431,989,000	1,576,608,000	53,211,000
Allowance for loan losses	(48,021,000)	(58,884,000)	(610,000)
Adjustment to lower of cost or fair value			(321,000)
Net loans	1,383,968,000	1,517,724,000	52,280,000
Deposits [Abstract]
Non-interest bearing	485,109,000	497,718,000	66,392,000
Savings and interest-bearing checking	853,603,000	1,019,603,000	225,062,000
Retail time	377,085,000	526,525,000	117,180,000
Total deposits			408,634,000
Net adjustments			(2,784,000)
Total Deposits	1,764,656,000	2,086,125,000	405,850,000
Deposit premium payment	11,800,000
Percentage of deposit premium on identified core deposits (in hundredths)	3.00%
Discount percentage of branches being sold (in hundredths)	1.75%
Fair value of fixed assets expected to be sold	8,400,000
Cost of fixed assets expected to be sold, net of accumulated depreciation	10,900,000
Amount of remaining unamortized intangible assets	2,600,000
Estimated gain on Branch sale	5,800,000
Estimated existing core deposit intangibles allocation related to Branch sale	2,600,000
Estimated loss on sale of fixed assets allocation related to Branch sale	2,500,000
Estimated loss on the sale of loans allocation related to Branch sale	300,000
Estimated transaction related costs allocation related to Branch sale	$ 600,000