Pension and Other Postretirement Benefit Plans (Details Textual) (USD $) In Millions, unless otherwise specified	6 Months Ended		3 Months Ended			6 Months Ended
	Jun. 30, 2012	Jun. 30, 2012 Minimum [Member]	Mar. 31, 2012 Contribution to corporation's pension plan [Member]	Jun. 30, 2012 Chemical Financial Corporation [Member]	Jun. 30, 2011 Chemical Financial Corporation [Member]	Jun. 30, 2012 Chemical Financial Corporation [Member]	Jun. 30, 2011 Chemical Financial Corporation [Member]
Defined Benefit Plan Disclosure [Line Items]
Contribution to pension plan		$ 0.4	$ 12.0
Percentage of eligible pay contribution to certain employees						4.00%
Compensation contributions and a 4% of eligible pay contribution to certain employees who are not grandfathered under the pension plan				0.8	0.7	1.5	1.4
Pension and Other Postretirement Benefit Plans (Textual) [Abstract]
Corporations pension plan available credit balance	$ 0