Retirement Plans (Textual) (Details) (USD $)	12 Months Ended			1 Months Ended	12 Months Ended				12 Months Ended		12 Months Ended		12 Months Ended				12 Months Ended						1 Months Ended	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Jan. 31, 2012 Defined Benefit Pension Plan [Member]	Dec. 31, 2012 Defined Benefit Pension Plan [Member] employee	Dec. 31, 2011 Defined Benefit Pension Plan [Member]	Dec. 31, 2010 Defined Benefit Pension Plan [Member]	Jun. 30, 2006 Defined Benefit Pension Plan [Member]	Dec. 31, 2012 Defined Benefit Pension Plan [Member] Equity securities [Member]	Dec. 31, 2011 Defined Benefit Pension Plan [Member] Equity securities [Member]	Dec. 31, 2012 Defined Benefit Pension Plan [Member] Debt securities [Member]	Dec. 31, 2011 Defined Benefit Pension Plan [Member] Debt securities [Member]	Dec. 31, 2012 Defined Benefit Pension Plan [Member] Other securities [Member]	Dec. 31, 2011 Defined Benefit Pension Plan [Member] Other securities [Member]	Dec. 31, 2012 Defined Benefit Pension Plan [Member] Common Stock [Member]	Dec. 31, 2011 Defined Benefit Pension Plan [Member] Common Stock [Member]	Dec. 31, 2012 Supplemental Plan [Member]	Dec. 31, 2011 Supplemental Plan [Member]	Dec. 31, 2010 Supplemental Plan [Member]	Dec. 31, 2012 Postretirement Plan [Member]	Dec. 31, 2011 Postretirement Plan [Member]	Dec. 31, 2010 Postretirement Plan [Member]	Jan. 31, 2013 Subsequent Event [Member] Defined Benefit Pension Plan [Member]	Dec. 31, 2012 Chemical Financial Corporation [Member] Defined Benefit Pension Plan [Member] Common Stock [Member]	Dec. 31, 2011 Chemical Financial Corporation [Member] Defined Benefit Pension Plan [Member] Common Stock [Member]
Defined Benefit Plan Disclosure [Line Items]
Percentage of Salaried Employees whose Pension Benefits were Frozen								0.67
Maximum years of vested service for calculation of retirement benefits					30 years
Years of employees highest average salary for calculation of retirement benefits					5 years
Number of years preceding retirement for calculation of retirement benefits					10 years
Maximum years of service for which pension benefits calculation is based upon vested service and average five years of salary					15 years
Maximum total years of age and years of service for which pension benefits calculation is based upon vested service and average five years of salary					65 years
Number of employees covered by the pension plan					214
Percentage of eligible pay contribution to certain employees	4.00%
Employer contributions				$ 12,000,000	$ 12,000,000	$ 0														$ 218,000	$ 144,000		$ 15,000,000
Minimum pension plan contributions required in 2013					1,800,000
Target plan asset allocations range - minimum									60.00%		30.00%		0.00%
Target plan asset allocations range - maximum									70.00%		40.00%		10.00%
Common stock, shares issued	27,498,868	27,456,907													210,663	221,663
Dividends paid	22,566,000	21,964,000	21,243,000																					180,000	180,000
Fair value of common stock															5,000,000	4,700,000
Pension plan actual asset allocations					100.00%	100.00%			70.00%	71.00%	28.00%	27.00%	2.00%	2.00%	5.10%	5.70%
Projected benefit obligation					115,177,000	100,216,000	86,704,000										1,600,000	1,300,000		3,243,000	3,290,000	3,757,000
Accumulated benefit obligation					108,078,000	94,089,000											1,400,000	1,100,000		3,243,000	3,290,000
Plan expense																	$ 200,000	$ 100,000	$ 100,000
Minimum retirement age (years)																				50 years
Maximum benefit age of spouse (years)																				65 years
Minimum retirement age with twenty-five years of service to be eligible for postretirement benefits (years)																				60 years
Minimum years of service for retirees at age sixty to be eligible for postretirement benefits (years)																				25 years
Expected health care cost trend rate assumed for 2013																				8.00%
Expected ultimate health care cost trend rate in 2016																				5.00%