Summary of Significant Accounting Policies (Detail Textuals 1)	3 Months Ended
	Mar. 31, 2016 USD ($)
Significant Accounting Policies [Line Items]
Acquired goodwill	$ 8,244,000
Coyote Creek Mining Company, L.L.C. (CCMC) | Lignite Sales Agreement | Otter Tail Power Company
Significant Accounting Policies [Line Items]
Amortization period	52 months
Percentage of development period costs, development fees and capital charge incurred by CCMC	35.00%
Amount of development period costs, development fees and capital charges incurred by CCMC	$ 60,300,000
Maximum exposure to loss as a result of involvement with CCMC	$ 60,300,000