Regulatory Assets and Liabilities (Detail Textuals)	6 Months Ended
	Jun. 30, 2013
Debt Reacquisition Premiums
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory Assets - Long Term, Remaining Recovery/Refund Period	231 months
Otter Tail Power Company | South Dakota - Nonasset-Based Margin Sharing Excess
Schedule of Regulatory Assets and Liabilities [Line Items]
Share of actual profit margins on nonasset-based wholesale sales of electricity	25.00%