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v3.19.3.a.u2

Note 1 - Summary of Significant Accounting Policies (Details Textual) - USD ($) |  | 12 Months Ended
--- | --- | ---
Jan. 01, 2019 | Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Standard Product Warranty Term |  | 1 year |  |
Standard Product Warranty Accrual, Decrease for Payments |  | $ 0 | $ 0 | $ 0
Accounting Standards Update 2018-02 [Member] |  |  |  |
Tax Cuts and Jobs Act, Reclassification from AOCI to Retained Earnings, Tax Effect | $ 784,000 |  |  |
Otter Tail Power Company [Member] | Coyote Creek Mining Company, L.L.C. (CCMC) [Member] | Lignite Sales Agreement [Member] |  |  |  |
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount |  | $ 50,400,000 |  |
Variable Interest Entity Reporting Entity Involvement, Maximum Loss Exposure, Percentage |  | 35.00% |  |
Electric Plant [Member] |  |  |  |
Interest Costs Capitalized |  | $ 1,728,000 | $ 1,206,000 | $ 741,000
Public Utilities, Property, Plant and Equipment, Disclosure of Composite Depreciation Rate for Plants in Service |  | 2.81% | 2.76% | 2.74%
Electric Plant [Member] | Minimum [Member] |  |  |  |
Property, Plant and Equipment, Useful Life |  | 5 years |  |
Electric Plant [Member] | Maximum [Member] |  |  |  |
Property, Plant and Equipment, Useful Life |  | 82 years |  |
Nonelectric Plant [Member] |  |  |  |
Interest Costs Capitalized |  | $ 0 | $ 0 | $ 0
Nonelectric Plant [Member] | Minimum [Member] |  |  |  |
Property, Plant and Equipment, Useful Life |  | 2 years |  |
Nonelectric Plant [Member] | Maximum [Member] |  |  |  |
Property, Plant and Equipment, Useful Life |  | 40 years |  |

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