Note 1 - Summary of Significant Accounting Policies (Details Textual) - Coyote Creek Mining Company, L.L.C. (CCMC) [Member] - Otter Tail Power Company [Member] - Lignite Sales Agreement [Member] $ in Millions	6 Months Ended
	Jun. 30, 2017 USD ($)
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount	$ 58.9
Variable Interest Entity Reporting Entity Involvement, Maximum Loss Exposure, Percentage	35.00%