Pension and Other Postretirement Benefit Plans (Details Textual) (USD $) In Millions, unless otherwise specified	9 Months Ended	3 Months Ended	9 Months Ended
Sep. 30, 2012 Minimum [Member]	Mar. 31, 2012 Contribution to corporation's pension plan [Member]	Sep. 30, 2012 Chemical Financial Corporation [Member]	Sep. 30, 2011 Chemical Financial Corporation [Member]	Sep. 30, 2012 Chemical Financial Corporation [Member]	Sep. 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	$ 2.3	$ 2.1

The increase in the fair value of plan assets from contributions made by the employer.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 132R

-Paragraph 5

-Subparagraph b

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (b)(3)

-URI http://asc.fasb.org/extlink&oid=21915506&loc=d3e1928-114920

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration