Regulatory Capital (Details) (USD $)	Sep. 30, 2012	Dec. 31, 2011	Sep. 30, 2011
Regulatory Capital (Textual) [Abstract]
Risk weighted assets	$ 4,030,000,000	$ 3,880,000,000	$ 3,780,000,000
Dividend pay	13,200,000
Chemical Financial Corporation [Member]
Total Capital to Risk-Weighted Assets:
Actual, Capital Amount	549,388,000	517,547,000	493,976,000
Minimum Required for Capital Adequacy Purposes, Capital Amount	322,212,000	310,316,000	302,360,000
Actual, Ratio	13.60%	13.30%	13.10%
Minimum Required for Capital Adequacy Purposes, Ratio	8.00%	8.00%	8.00%
Tier 1 Capital to Risk-Weighted Assets:
Actual, Capital Amount	498,618,000	468,565,000	446,217,000
Minimum Required for Capital Adequacy Purposes, Capital Amount	161,106,000	155,158,000	151,180,000
Actual, Ratio	12.40%	12.10%	11.80%
Minimum Required for Capital Adequacy Purposes, Ratio	4.00%	4.00%	4.00%
Leverage Ratio:
Actual, Capital Amount	498,618,000	468,565,000	446,217,000
Minimum Required for Capital Adequacy Purposes, Capital Amount	211,670,000	208,013,000	206,656,000
Actual, Ratio	9.40%	9.00%	8.60%
Minimum Required for Capital Adequacy Purposes, Ratio	4.00%	4.00%	4.00%
Chemical Bank [Member]
Total Capital to Risk-Weighted Assets:
Actual, Capital Amount	537,467,000	510,290,000	486,207,000
Minimum Required for Capital Adequacy Purposes, Capital Amount	321,585,000	310,119,000	302,149,000
Required to be Well Capitalized Under Prompt Corrective Action Regulations, Capital Amount	401,982,000	387,649,000	377,686,000
Actual, Ratio	13.40%	13.20%	12.90%
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	486,794,000	461,338,000	438,480,000
Minimum Required for Capital Adequacy Purposes, Capital Amount	160,793,000	155,060,000	151,074,000
Required to be Well Capitalized Under Prompt Corrective Action Regulations, Capital Amount	241,189,000	232,589,000	226,612,000
Actual, Ratio	12.10%	11.90%	11.60%
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	486,794,000	461,338,000	438,480,000
Minimum Required for Capital Adequacy Purposes, Capital Amount	211,452,000	208,033,000	206,613,000
Required to be Well Capitalized Under Prompt Corrective Action Regulations, Capital Amount	$ 264,315,000	$ 260,042,000	$ 258,266,000
Actual, Ratio	9.20%	8.90%	8.50%
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%

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Dividend Availability Under Regulatory Requirements

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The amount of total capital as defined in the regulations.

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The minimum amount of Total Capital required for capital adequacy purposes under the regulatory framework for prompt corrective action.

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The minimum Total risk based capital ratio (total capital divided by risk weighted assets) required for capital adequacy purposes under the regulatory framework for prompt corrective action.

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The amount of Total Capital required to be categorized as well as capitalized under the regulatory framework for prompt corrective action.

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The Total risk based capital ratio (total capital divided by risk weighted assets) required to be categorized as "well capitalized", in the regulatory framework for prompt corrective action.

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Total Capital divided by risk weighted assets as defined in the regulations.

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Amount of risk-weighted assets as calculated in accordance with U.S. Federal regulatory capital standards.

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Tier 1 Leverage Capital as defined in the regulations. Also called Core Capital.

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The minimum amount of Tier 1 Leverage Capital required for capital adequacy purposes under the regulatory framework for prompt corrective action.

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The minimum amount of Tier 1 Leverage Capital for capital adequacy purposes divided by average assets as defined in the regulations.

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The amount of Tier 1 Leverage Capital required to be categorized as well capitalized divided by average assets as defined in the regulatory framework for prompt corrective action.

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Tier 1 Leverage Capital divided by average assets as defined in the regulations.

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Tier 1 Risk Based Capital as defined in the regulations.

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The minimum amount of Tier 1 Risk Based Capital required for capital adequacy purposes under the regulatory framework for prompt corrective action.

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The minimum Tier One Capital Ratio (Tier one capital divided by risk-weighted assets) required for capital adequacy purposes under the regulatory framework for prompt corrective action.

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The amount of Tier 1 Risk Based Capital required to be categorized as well capitalized under the regulatory framework for prompt corrective action.

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Tier 1 capital divided by risk weighted assets as defined by regulations.

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