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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		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Revenues recorded under rate riders	$ 11,258	$ 4,399	$ 28,440	$ 15,816
Renewable Resource Adjustment [Member] | Minnesota1 [Member]
Revenues recorded under rate riders	3,318	1,316	9,660	3,949
Renewable Resource Adjustment [Member] | North Dakota 1 [Member]
Revenues recorded under rate riders	1,256	(20)	3,455	616
Conservation Improvement Program Costs and Incentives [Member] | Minnesota1 [Member]
Revenues recorded under rate riders	2,096	1,518	4,703	4,246
Conservation Improvement Program Costs and Incentives [Member] | South Dakota 1 [Member]
Revenues recorded under rate riders	194	100	748	440
Transmission Cost Recovery Rider [Member] | Minnesota1 [Member]
Revenues recorded under rate riders	2,001	(284)	2,402	301
Transmission Cost Recovery Rider [Member] | North Dakota 1 [Member]
Revenues recorded under rate riders	809	908	3,131	3,554
Transmission Cost Recovery Rider [Member] | South Dakota 1 [Member]
Revenues recorded under rate riders	450	743	1,383	1,587
Environmental Cost Recovery Rider [Member] | Minnesota1 [Member]
Revenues recorded under rate riders	0	0	0	(1)
Environmental Cost Recovery Rider [Member] | North Dakota 1 [Member]
Revenues recorded under rate riders	0	(7)	0	556
Environmental Cost Recovery Rider [Member] | South Dakota 1 [Member]
Revenues recorded under rate riders	0	(2)	0	(29)
Generation Cost Recovery [Member] | North Dakota 1 [Member]
Revenues recorded under rate riders	1,187	137	3,035	607
Phase-In Rate Plan [Member] | South Dakota 1 [Member]
Revenues recorded under rate riders	$ (53)	$ (10)	$ (77)	$ (10)

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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