Parent Company Only Financial Statements Financial Position (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Assets [Abstract]
Investment securities available-for-sale	$ 586,809	$ 667,276
Premises and equipment	75,458	65,997
Goodwill	120,164	113,414
Other assets	132,412	154,245
Total Assets	5,917,252	5,339,453
Liabilities and Equity [Abstract]
Other liabilities	54,716	54,024
Shareholders' equity	596,341	571,729	560,078	474,311
Total Liabilities and Shareholders' Equity	5,917,252	5,339,453
Chemical Financial Corporation [Member]
Assets [Abstract]
Cash at subsidiary bank	5,960	4,481
Investment securities available-for-sale	4,755	0
Investment in subsidiary bank	579,448	559,410
Premises and equipment	4,309	4,625
Goodwill	1,092	1,092
Other assets	2,598	3,631
Total Assets	598,162	573,239
Liabilities and Equity [Abstract]
Other liabilities	1,821	1,510
Shareholders' equity	596,341	571,729
Total Liabilities and Shareholders' Equity	$ 598,162	$ 573,239