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Note 3 - Rate and Regulatory Matters - Summary of Status of Updates for Previous Two Years for Various Rate Riders (Details) - Otter Tail Power Company [Member] $ in Thousands | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2020 USD ($) | Jun. 30, 2019 USD ($) | Jun. 30, 2020 USD ($) kWh | Jun. 30, 2019 USD ($)
Annual Revenue | $ 7,016 | $ 4,537 | $ 17,182 | $ 11,417
Minnesota1 [Member] | Conservation Improvement Program Costs and Incentives [Member] |  |  |  |
Annual Revenue | 1,521 | 1,841 | $ 2,607 | 2,728
Minnesota1 [Member] | Conservation Improvement Program Costs and Incentives [Member] | The 2019 Incentive and Cost Recovery [Member] |  |  |  |
Request date |  |  | May 01, 2020 |
Effective Date Requested or Approved |  |  | Oct. 01, 2020 |
Annual Revenue |  |  | $ 8,247 |
Rate rider rate (Kilowatt-Hour) | kWh |  |  | 0.00485 |
Request date |  |  | May 01, 2020 |
Effective Date Requested or Approved |  |  | Oct. 01, 2020 |
Minnesota1 [Member] | Conservation Improvement Program Costs and Incentives [Member] | The 2018 Incentive and Cost Recovery [Member] |  |  |  |
Effective Date Requested or Approved |  |  | Jan. 01, 2020 |
Annual Revenue |  |  | $ 11,926 |
Rate rider rate (Kilowatt-Hour) | kWh |  |  | 0.00710 |
Approval date |  |  | Dec. 27, 2019 |
Effective Date Requested or Approved |  |  | Jan. 01, 2020 |
Minnesota1 [Member] | Conservation Improvement Program Costs and Incentives [Member] | The 2017 Incentive and Cost Recovery [Member] |  |  |  |
Effective Date Requested or Approved |  |  | Nov. 01, 2018 |
Annual Revenue |  |  | $ 10,283 |
Rate rider rate (Kilowatt-Hour) | kWh |  |  | 0.00600 |
Approval date |  |  | Oct. 04, 2018 |
Effective Date Requested or Approved |  |  | Nov. 01, 2018 |
Minnesota1 [Member] | Transmission Cost Recovery Rider [Member] |  |  |  |
Annual Revenue | (314) | (56) | $ 401 | 585
Minnesota1 [Member] | Transmission Cost Recovery Rider [Member] | The 2018 Annual Update [Member] |  |  |  |
Request date |  |  | May 07, 2020 |
Effective Date Requested or Approved |  |  | Jan. 01, 2021 |
Annual Revenue |  |  | $ 10,264 |
Request date |  |  | May 07, 2020 |
Effective Date Requested or Approved |  |  | Jan. 01, 2021 |
Minnesota1 [Member] | Transmission Cost Recovery Rider [Member] | The 2017 Rate Reset [Member] |  |  |  |
Effective Date Requested or Approved |  |  | Nov. 01, 2017 |
Annual Revenue |  |  | $ (3,311) |
Approval date |  |  | Oct. 30, 2017 |
Effective Date Requested or Approved |  |  | Nov. 01, 2017 |
Minnesota1 [Member] | Environmental Cost Recovery Rider [Member] |  |  |  |
Annual Revenue | 0 | 0 | $ 0 | (1)
Minnesota1 [Member] | Environmental Cost Recovery Rider [Member] | The 2018 Annual Update [Member] |  |  |  |
Effective Date Requested or Approved |  |  | Dec. 01, 2018 |
Annual Revenue |  |  | $ 0 |
Approval date |  |  | Nov. 29, 2018 |
Effective Date Requested or Approved |  |  | Dec. 01, 2018 |
Rate of base |  |  | 0.00% |
Minnesota1 [Member] | Renewable Resource Adjustment [Member] |  |  |  |
Annual Revenue | 3,088 | 1,317 | $ 6,342 | 2,633
Minnesota1 [Member] | Renewable Resource Adjustment [Member] | The 2018 Annual Update [Member] |  |  |  |
Effective Date Requested or Approved |  |  | Nov. 01, 2018 |
Annual Revenue |  |  | $ 5,886 |
Rate rider rate (Kilowatt-Hour) | kWh |  |  | 0.00219 |
Approval date |  |  | Aug. 29, 2018 |
Effective Date Requested or Approved |  |  | Nov. 01, 2018 |
Minnesota1 [Member] | Renewable Resource Adjustment [Member] | The 2019 Annual Update - Revised [Member] |  |  |  |
Effective Date Requested or Approved |  |  | Jan. 01, 2020 |
Annual Revenue |  |  | $ 12,506 |
Rate rider rate (Kilowatt-Hour) | kWh |  |  | 0.00467 |
Approval date |  |  | Dec. 19, 2019 |
Effective Date Requested or Approved |  |  | Jan. 01, 2020 |
North Dakota 1 [Member] | Transmission Cost Recovery Rider [Member] |  |  |  |
Annual Revenue | 840 | 874 | $ 2,322 | 2,646
North Dakota 1 [Member] | Transmission Cost Recovery Rider [Member] | The 2019 Annual Update [Member] |  |  |  |
Effective Date Requested or Approved |  |  | Jan. 01, 2020 |
Annual Revenue |  |  | $ 5,739 |
Approval date |  |  | Dec. 18, 2019 |
Effective Date Requested or Approved |  |  | Jan. 01, 2020 |
North Dakota 1 [Member] | Transmission Cost Recovery Rider [Member] | The 2018 Rate Reset for Effect of TCJA [Member] |  |  |  |
Effective Date Requested or Approved |  |  | Mar. 01, 2018 |
Annual Revenue |  |  | $ 7,469 |
Approval date |  |  | Feb. 27, 2018 |
Effective Date Requested or Approved |  |  | Mar. 01, 2018 |
North Dakota 1 [Member] | Transmission Cost Recovery Rider [Member] | The 2018 Supplemental Update [Member] |  |  |  |
Effective Date Requested or Approved |  |  | Feb. 01, 2019 |
Annual Revenue |  |  | $ 4,801 |
Approval date |  |  | Dec. 06, 2018 |
Effective Date Requested or Approved |  |  | Feb. 01, 2019 |
North Dakota 1 [Member] | Environmental Cost Recovery Rider [Member] |  |  |  |
Annual Revenue | 0 | (12) | $ 0 | 563
North Dakota 1 [Member] | Environmental Cost Recovery Rider [Member] | The 2018 Annual Update [Member] |  |  |  |
Effective Date Requested or Approved |  |  | Feb. 01, 2019 |
Annual Revenue |  |  | $ (378) |
Approval date |  |  | Dec. 19, 2018 |
Effective Date Requested or Approved |  |  | Feb. 01, 2019 |
Rate of base |  |  | (0.31%) |
North Dakota 1 [Member] | Environmental Cost Recovery Rider [Member] | The 2019 Annual Update [Member] |  |  |  |
Effective Date Requested or Approved |  |  | Nov. 01, 2019 |
Annual Revenue |  |  | $ 0 |
Approval date |  |  | Oct. 22, 2019 |
Effective Date Requested or Approved |  |  | Nov. 01, 2019 |
Rate of base |  |  | 0.00% |
North Dakota 1 [Member] | Environmental Cost Recovery Rider [Member] | The 2018 Rate Reset for Effect of TCJA [Member] |  |  |  |
Effective Date Requested or Approved |  |  | Mar. 01, 2018 |
Annual Revenue |  |  | $ 7,718 |
Approval date |  |  | Feb. 27, 2018 |
Effective Date Requested or Approved |  |  | Mar. 01, 2018 |
Rate of base |  |  | 5.593% |
North Dakota 1 [Member] | Renewable Resource Adjustment [Member] |  |  |  |
Annual Revenue | 1,070 | (93) | $ 2,199 | 636
North Dakota 1 [Member] | Renewable Resource Adjustment [Member] | The 2020 Annual Update [Member] |  |  |  |
Effective Date Requested or Approved |  |  | Apr. 01, 2020 |
Annual Revenue |  |  | $ 5,762 |
Approval date |  |  | Mar. 18, 2020 |
Effective Date Requested or Approved |  |  | Apr. 01, 2020 |
Rate of base |  |  | 5.637% |
North Dakota 1 [Member] | Renewable Resource Adjustment [Member] | The 2019 Annual Update [Member] |  |  |  |
Effective Date Requested or Approved |  |  | Jun. 01, 2019 |
Annual Revenue |  |  | $ (235) |
Approval date |  |  | May 01, 2019 |
Effective Date Requested or Approved |  |  | Jun. 01, 2019 |
Rate of base |  |  | (0.224%) |
North Dakota 1 [Member] | Renewable Resource Adjustment [Member] | The 2018 Rate Reset for Effect of TCJA [Member] |  |  |  |
Effective Date Requested or Approved |  |  | Mar. 01, 2018 |
Annual Revenue |  |  | $ 9,650 |
Approval date |  |  | Feb. 27, 2018 |
Effective Date Requested or Approved |  |  | Mar. 01, 2018 |
Rate of base |  |  | 7.493% |
North Dakota 1 [Member] | Generation Cost Recovery [Member] |  |  |  |
Annual Revenue | 900 | 222 | $ 1,848 | 470
North Dakota 1 [Member] | Generation Cost Recovery [Member] | The 2020 Annual Update [Member] |  |  |  |
Request date |  |  | Jun. 10, 2020 |
Effective Date Requested or Approved |  |  | Jul. 01, 2020 |
Annual Revenue |  |  | $ 6,184 |
Request date |  |  | Jun. 10, 2020 |
Effective Date Requested or Approved |  |  | Jul. 01, 2020 |
Rate of base |  |  | 6.041% |
North Dakota 1 [Member] | Generation Cost Recovery [Member] | The 2019 Initial Request [Member] |  |  |  |
Effective Date Requested or Approved |  |  | Jul. 01, 2019 |
Annual Revenue |  |  | $ 2,720 |
Approval date |  |  | May 15, 2019 |
Effective Date Requested or Approved |  |  | Jul. 01, 2019 |
Rate of base |  |  | 2.547% |
South Dakota 1 [Member] | Conservation Improvement Program Costs and Incentives [Member] |  |  |  |
Annual Revenue | 210 | 96 | $ 554 | 340
South Dakota 1 [Member] | Transmission Cost Recovery Rider [Member] |  |  |  |
Annual Revenue | 371 | 371 | $ 933 | 844
South Dakota 1 [Member] | Transmission Cost Recovery Rider [Member] | The 2020 Annual Update [Member] |  |  |  |
Effective Date Requested or Approved |  |  | Mar. 01, 2020 |
Annual Revenue |  |  | $ 2,327 |
Approval date |  |  | Feb. 19, 2020 |
Effective Date Requested or Approved |  |  | Mar. 01, 2020 |
South Dakota 1 [Member] | Transmission Cost Recovery Rider [Member] | The 2019 Annual Update [Member] |  |  |  |
Effective Date Requested or Approved |  |  | Mar. 01, 2019 |
Annual Revenue |  |  | $ 1,638 |
Approval date |  |  | Feb. 20, 2019 |
Effective Date Requested or Approved |  |  | Mar. 01, 2019 |
South Dakota 1 [Member] | Transmission Cost Recovery Rider [Member] | The 2019 Rate Reset [Member] |  |  |  |
Effective Date Requested or Approved |  |  | Oct. 01, 2019 |
Annual Revenue |  |  | $ 2,046 |
Approval date |  |  | Sep. 17, 2019 |
Effective Date Requested or Approved |  |  | Oct. 01, 2019 |
South Dakota 1 [Member] | Transmission Cost Recovery Rider [Member] | The 2018 Interim Rate Reset [Member] |  |  |  |
Effective Date Requested or Approved |  |  | Oct. 18, 2018 |
Annual Revenue |  |  | $ 1,171 |
Approval date |  |  | Oct. 18, 2018 |
Effective Date Requested or Approved |  |  | Oct. 18, 2018 |
South Dakota 1 [Member] | Environmental Cost Recovery Rider [Member] |  |  |  |
Annual Revenue | 0 | (23) | $ 0 | (27)
South Dakota 1 [Member] | Environmental Cost Recovery Rider [Member] | The 2018 Interim Rate Reset [Member] |  |  |  |
Effective Date Requested or Approved |  |  | Oct. 18, 2018 |
Annual Revenue |  |  | $ (189) |
Rate rider rate (Kilowatt-Hour) | kWh |  |  | (0.00075) |
Approval date |  |  | Oct. 18, 2018 |
Effective Date Requested or Approved |  |  | Oct. 18, 2018 |
South Dakota 1 [Member] | Phase-in Rate Plan Recovery [Member] | The 2020 Annual Update [Member] |  |  |  |
Request date |  |  | Jun. 01, 2020 |
Effective Date Requested or Approved |  |  | Sep. 01, 2020 |
Annual Revenue |  |  | $ 1,931 |
Request date |  |  | Jun. 01, 2020 |
Effective Date Requested or Approved |  |  | Sep. 01, 2020 |
Rate of base |  |  | 7.753% |
South Dakota 1 [Member] | Phase-In Rate Plan [Member] |  |  |  |
Annual Revenue | $ (670) | $ 0 | $ (24) | $ 0
South Dakota 1 [Member] | Phase-In Rate Plan [Member] | The 2019 Initial Request [Member] |  |  |  |
Effective Date Requested or Approved |  |  | Sep. 01, 2019 |
Annual Revenue |  |  | $ 864 |
Approval date |  |  | Aug. 21, 2019 |
Effective Date Requested or Approved |  |  | Sep. 01, 2019 |
Rate of base |  |  | 3.345% |

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