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Note 3 - Rate and Regulatory Matters - Summary of Revenues Recorded Under Rate Riders (Details) - Otter Tail Power Company [Member] - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Revenues recorded under rate riders	$ 10,166	$ 6,880
Renewable Resource Adjustment [Member] | Minnesota1 [Member]
Revenues recorded under rate riders	3,254	1,316
Renewable Resource Adjustment [Member] | North Dakota 1 [Member]
Revenues recorded under rate riders	1,129	729
Conservation Improvement Program Costs and Incentives [Member] | Minnesota1 [Member]
Revenues recorded under rate riders	1,086	887
Conservation Improvement Program Costs and Incentives [Member] | South Dakota 1 [Member]
Revenues recorded under rate riders	344	244
Transmission Cost Recovery Rider [Member] | Minnesota1 [Member]
Revenues recorded under rate riders	715	641
Transmission Cost Recovery Rider [Member] | North Dakota 1 [Member]
Revenues recorded under rate riders	1,482	1,772
Transmission Cost Recovery Rider [Member] | South Dakota 1 [Member]
Revenues recorded under rate riders	562	473
Environmental Cost Recovery Rider [Member] | Minnesota1 [Member]
Revenues recorded under rate riders	0	(1)
Environmental Cost Recovery Rider [Member] | North Dakota 1 [Member]
Revenues recorded under rate riders	0	575
Environmental Cost Recovery Rider [Member] | South Dakota 1 [Member]
Revenues recorded under rate riders	0	(4)
Generation Cost Recovery [Member] | North Dakota 1 [Member]
Revenues recorded under rate riders	948	248
Phase-In Rate Plan [Member] | South Dakota 1 [Member]
Revenues recorded under rate riders	$ 646	$ 0

X

- Definition

Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).

+ References

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