Note 5 - Open Contract Positions Subject to Legally Enforceable Netting Arrangements - Breakdown of OTP's Credit Risk Standing (Details) - Otter Tail Power Company [Member] - USD ($) $ in Thousands		Jun. 30, 2017	Dec. 31, 2016
Loss Contracts Covered by Deposited Funds or Letters of Credit
Contracts Requiring Cash Deposits if OTP's Credit Falls Below Investment Grade	[1]	13,856	17,382
Total Loss Contracts based on Current Market Values		$ 13,856	$ 17,382

[1] Certain OTP derivative energy contracts contain provisions that require an investment grade credit rating from each of the major credit rating agencies on OTP's debt. If OTP's debt ratings were to fall below investment grade, the counterparties to these forward energy contracts could request the immediate deposit of cash to cover contracts in net liability positions. Contracts Requiring Cash Deposits if OTP's Credit Falls Below Investment Grade $13,856 $17,382 Offsetting Gains with Counterparties under Master Netting Agreements -- --Reporting Date Deposit Requirement if Credit Risk Feature Triggered $13,856 $17,382