Regulatory Capital and Reserve Requirements (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Minimum average regulatory cash reserve balance	$ 27,900,000	$ 28,600,000
Cash dividends paid to parent company			21,300,000
Risk weighted assets	4,180,000,000	3,880,000,000
Chemical Financial Corporation [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Cash dividends paid to parent company	27,550,000	22,000,000	21,300,000
Total Capital to Risk-Weighted Assets:
Actual, Capital Amount	552,171,000	517,547,000
Minimum Required for Capital Adequacy Purposes, Capital Amount	334,140,000	310,316,000
Actual, Ratio	13.20%	13.30%
Minimum Required for Capital Adequacy Purposes, Ratio	8.00%	8.00%
Tier 1 Capital to Risk-Weighted Assets:
Actual, Capital Amount	499,563,000	468,565,000
Minimum Required for Capital Adequacy Purposes, Capital Amount	167,070,000	155,158,000
Actual, Ratio	12.00%	12.10%
Minimum Required for Capital Adequacy Purposes, Ratio	4.00%	4.00%
Leverage Ratio:
Actual, Capital Amount	499,563,000	468,565,000
Minimum Required for Capital Adequacy Purposes, Capital Amount	217,145,000	208,013,000
Actual, Ratio	9.20%	9.00%
Minimum Required for Capital Adequacy Purposes, Ratio	4.00%	4.00%
Chemical Bank [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Cash dividends paid to parent company	27,600,000	22,000,000
Dividend availability without regulatory approval	49,100,000
Total Capital to Risk-Weighted Assets:
Actual, Capital Amount	536,223,000	510,290,000
Minimum Required for Capital Adequacy Purposes, Capital Amount	333,195,000	310,119,000
Required to be Well Capitalized Under Prompt Corrective Action Regulations, Capital Amount	416,494,000	387,649,000
Actual, Ratio	12.90%	13.20%
Minimum Required for Capital Adequacy Purposes, Ratio	8.00%	8.00%
Required to be Well Capitalized Under Prompt Corrective Action Regulations, Ratio	10.00%	10.00%
Tier 1 Capital to Risk-Weighted Assets:
Actual, Capital Amount	483,761,000	461,338,000
Minimum Required for Capital Adequacy Purposes, Capital Amount	166,598,000	155,060,000
Required to be Well Capitalized Under Prompt Corrective Action Regulations, Capital Amount	249,896,000	232,589,000
Actual, Ratio	11.60%	11.90%
Minimum Required for Capital Adequacy Purposes, Ratio	4.00%	4.00%
Required to be Well Capitalized Under Prompt Corrective Action Regulations, Ratio	6.00%	6.00%
Leverage Ratio:
Actual, Capital Amount	483,761,000	461,338,000
Minimum Required for Capital Adequacy Purposes, Capital Amount	216,784,000	208,033,000
Required to be Well Capitalized Under Prompt Corrective Action Regulations, Capital Amount	$ 270,980,000	$ 260,042,000
Actual, Ratio	8.90%	8.90%
Minimum Required for Capital Adequacy Purposes, Ratio	4.00%	4.00%
Required to be Well Capitalized Under Prompt Corrective Action Regulations, Ratio	5.00%	5.00%