Regulatory Capital (Details) (USD $)	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2012
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Risk weighted assets	$ 4,220,000,000	$ 4,180,000,000	$ 3,870,000,000
Chemical Financial Corporation [Member]
Total Capital to Risk-Weighted Assets:
Actual, Capital Amount	561,092,000	552,171,000	528,910,000
Minimum Required for Capital Adequacy Purposes, Capital Amount	337,508,000	334,140,000	309,209,000
Actual, Ratio	13.30%	13.20%	13.70%
Minimum Required for Capital Adequacy Purposes, Ratio	8.00%	8.00%	8.00%
Tier 1 Capital to Risk-Weighted Assets:
Actual, Capital Amount	507,985,000	499,563,000	480,109,000
Minimum Required for Capital Adequacy Purposes, Capital Amount	168,754,000	167,070,000	154,605,000
Actual, Ratio	12.00%	12.00%	12.40%
Minimum Required for Capital Adequacy Purposes, Ratio	4.00%	4.00%	4.00%
Leverage Ratio:
Actual, Capital Amount	507,985,000	499,563,000	481,109,000
Minimum Required for Capital Adequacy Purposes, Capital Amount	230,992,000	217,145,000	210,126,000
Actual, Ratio	8.80%	9.20%	9.10%
Minimum Required for Capital Adequacy Purposes, Ratio	4.00%	4.00%	4.00%
Chemical Bank [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Dividend availability without regulatory approval	57,200,000
Total Capital to Risk-Weighted Assets:
Actual, Capital Amount	545,361,000	536,223,000	522,775,000
Minimum Required for Capital Adequacy Purposes, Capital Amount	336,576,000	333,195,000	309,024,000
Required to be Well Capitalized Under Prompt Corrective Action Regulations, Capital Amount	420,720,000	416,494,000	386,280,000
Actual, Ratio	13.00%	12.90%	13.50%
Minimum Required for Capital Adequacy Purposes, Ratio	8.00%	8.00%	8.00%
Required to be Well Capitalized Under Prompt Corrective Action Regulations, Ratio	10.00%	10.00%	10.00%
Tier 1 Capital to Risk-Weighted Assets:
Actual, Capital Amount	492,398,000	483,761,000	474,002,000
Minimum Required for Capital Adequacy Purposes, Capital Amount	168,288,000	166,598,000	154,512,000
Required to be Well Capitalized Under Prompt Corrective Action Regulations, Capital Amount	252,432,000	249,896,000	231,768,000
Actual, Ratio	11.70%	11.60%	12.30%
Minimum Required for Capital Adequacy Purposes, Ratio	4.00%	4.00%	4.00%
Required to be Well Capitalized Under Prompt Corrective Action Regulations, Ratio	6.00%	6.00%	6.00%
Leverage Ratio:
Actual, Capital Amount	492,398,000	483,761,000	474,002,000
Minimum Required for Capital Adequacy Purposes, Capital Amount	230,544,000	216,784,000	210,055,000
Required to be Well Capitalized Under Prompt Corrective Action Regulations, Capital Amount	$ 288,179,000	$ 270,980,000	$ 262,569,000
Actual, Ratio	8.50%	8.90%	9.00%
Minimum Required for Capital Adequacy Purposes, Ratio	4.00%	4.00%	4.00%
Required to be Well Capitalized Under Prompt Corrective Action Regulations, Ratio	5.00%	5.00%	5.00%