Parent Company Only Financial Statements Statements of Income (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Condensed Financial Statements, Captions [Line Items]
Cash dividends from subsidiary bank											$ 21,300
Other income									1,236	462	280
Operating expenses	41,211	36,066	35,537	36,295	37,807	35,394	33,413	35,389	149,109	142,003	136,802
Federal income tax benefit	(4,000)	(5,300)	(6,325)	(5,175)	(4,475)	(4,075)	(4,750)	(3,900)	(20,800)	(17,200)	(8,100)
Net Income	11,662	13,106	13,866	12,374	11,204	11,625	11,033	9,188	51,008	43,050	23,090
Chemical Financial Corporation [Member]
Condensed Financial Statements, Captions [Line Items]
Cash dividends from subsidiary bank									27,550	22,000	21,300
Other income									92	0	0
Total income									27,642	22,000	21,300
Operating expenses									3,773	3,350	5,116
Income (loss) before income taxes and equity in undistributed net income of subsidiary bank									23,869	18,650	16,184
Federal income tax benefit									1,311	1,171	1,335
Equity in undistributed net income of subsidiary bank									25,828	23,229	5,571
Net Income									$ 51,008	$ 43,050	$ 23,090