Commitments and Contingencies (Detail Textuals) - USD ($)	9 Months Ended	12 Months Ended
	Sep. 30, 2016	Dec. 31, 2015	Sep. 27, 2016
Commitments and Contingencies Disclosure [Line Items]
Loss contingency, range of possible loss, maximum	$ 1,000,000
Otter Tail Power Company | Federal Energy Regulatory Commission
Commitments and Contingencies Disclosure [Line Items]
Estimated liability of refund obligation	$ 2,400,000
Otter Tail Power Company | Coal Purchase Commitments
Commitments and Contingencies Disclosure [Line Items]
Contracts expiration year	2017 and 2040
Otter Tail Power Company | Electric utility capacity
Commitments and Contingencies Disclosure [Line Items]
Commitment under contracts aggregate amount	$ 3,500,000
Otter Tail Power Company | Construction Programs
Commitments and Contingencies Disclosure [Line Items]
Commitment under contracts aggregate amount	$ 137,400,000	$ 89,600,000
Otter Tail Power Company | Operating lease | Rail cars used for transport of coal
Commitments and Contingencies Disclosure [Line Items]
Operating Leases			$ 970,000