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Note 4 - Regulatory Assets and Liabilities (Tables) | 12 Months Ended
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Dec. 31, 2019
Notes Tables |
Schedule of Regulatory Assets and Liabilities [Table Text Block] |
|  | December 31, 2019 |  |  | Remaining Recovery/ |
(in thousands) |  | Current |  |  | Long-Term |  |  | Total |  |  | Refund Period (months) |
Regulatory Assets: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Prior Service Costs and Actuarial Losses on Pensions and Other Postretirement Benefits1 |  | $ | 9,090 |  |  | $ | 129,102 |  |  | $ | 138,192 |  |  | see below |
Accumulated Asset Retirement Obligation (ARO) Accretion/Depreciation Adjustment1 |  |  | - |  |  |  | 7,772 |  |  |  | 7,772 |  |  | asset lives |
Conservation Improvement Program Costs and Incentives2 |  |  | 4,024 |  |  |  | 2,844 |  |  |  | 6,868 |  |  |  | 21 |
Minnesota Transmission Cost Recovery Rider Accrued Revenues2 |  |  | 4,208 |  |  |  | - |  |  |  | 4,208 |  |  |  | 12 |
MISO Schedule 26/26A Transmission Cost Recovery Rider True-ups1 |  |  | 2,033 |  |  |  | 968 |  |  |  | 3,001 |  |  |  | 24 |
Nonservice Costs Components of Postretirement Benefits Capitalized for Ratemaking Purposes and Subject to Deferred Recovery1 |  |  | - |  |  |  | 1,681 |  |  |  | 1,681 |  |  | asset lives |
Big Stone II Unrecovered Project Costs – Minnesota1 |  |  | 715 |  |  |  | 225 |  |  |  | 940 |  |  |  | 16 |
Debt Reacquisition Premiums1 |  |  | 201 |  |  |  | 548 |  |  |  | 749 |  |  |  | 153 |
Deferred Marked-to-Market Losses1 |  |  | 743 |  |  |  | - |  |  |  | 743 |  |  |  | 12 |
Big Stone II Unrecovered Project Costs – South Dakota1 |  |  | 144 |  |  |  | 253 |  |  |  | 397 |  |  |  | 33 |
South Dakota Deferred Rate Case Expenses Subject to Recovery1 |  |  | 138 |  |  |  | 245 |  |  |  | 383 |  |  |  | 34 |
North Dakota Deferred Rate Case Expenses Subject to Recovery1 |  |  | 122 |  |  |  | 244 |  |  |  | 366 |  |  |  | 36 |
Minnesota SPP Transmission Cost Recovery Tracker1 |  |  | - |  |  |  | 202 |  |  |  | 202 |  |  | see below |
Minnesota Renewable Resource Rider Accrued Revenues2 |  |  | 131 |  |  |  | - |  |  |  | 131 |  |  |  | 12 |
South Dakota Transmission Cost Recovery Rider Accrued Revenues2 |  |  | 97 |  |  |  | - |  |  |  | 97 |  |  |  | 2 |
Deferred Lease Expenses1 |  |  | - |  |  |  | 54 |  |  |  | 54 |  |  |  | 39 |
Minnesota Environmental Cost Recovery Rider Accrued Revenues2 |  |  | 4 |  |  |  | - |  |  |  | 4 |  |  |  | 12 |
Total Regulatory Assets |  | $ | 21,650 |  |  | $ | 144,138 |  |  | $ | 165,788 |  |  |  |  |
Regulatory Liabilities: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Deferred Income Taxes |  | $ | - |  |  | $ | 141,707 |  |  | $ | 141,707 |  |  | asset lives |
Accumulated Reserve for Estimated Removal Costs – Net of Salvage |  |  | - |  |  |  | 97,726 |  |  |  | 97,726 |  |  | asset lives |
Refundable Fuel Clause Adjustment Revenues |  |  | 3,982 |  |  |  | - |  |  |  | 3,982 |  |  |  | 12 |
North Dakota Renewable Resource Recovery Rider Accrued Refund |  |  | 1,515 |  |  |  | - |  |  |  | 1,515 |  |  |  | 12 |
North Dakota Transmission Cost Recovery Rider Accrued Refund |  |  | 700 |  |  |  | - |  |  |  | 700 |  |  |  | 12 |
Prior Service Costs and Actuarial Gains on Postretirement Benefits |  |  | 471 |  |  |  | - |  |  |  | 471 |  |  |  | 12 |
Revenue for Rate Case Expenses Subject to Refund – Minnesota |  |  | - |  |  |  | 401 |  |  |  | 401 |  |  | see below |
South Dakota Phase-In Rate Plan Rider Accrued Refund |  |  | 355 |  |  |  | - |  |  |  | 355 |  |  |  | 9 |
North Dakota Generation Cost Recovery Rider Accrued Refund |  |  | 287 |  |  |  | - |  |  |  | 287 |  |  |  | 6 |
Minnesota Energy Intensive Trade Exposed Rider Accrued Refund |  |  | 164 |  |  |  | - |  |  |  | 164 |  |  |  | 12 |
Other |  |  | 6 |  |  |  | 72 |  |  |  | 78 |  |  |  | 168 |
Total Regulatory Liabilities |  | $ | 7,480 |  |  | $ | 239,906 |  |  | $ | 247,386 |  |  |  |  |
Net Regulatory Asset/(Liability) Position |  | $ | 14,170 |  |  | $ | (95,768 | ) |  | $ | (81,598 | ) |  |  |  |
| December 31, 2018 | Remaining Recovery/ |
(in thousands) |  | Current |  |  | Long-Term |  |  | Total | Refund Period (months) |
Regulatory Assets: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Prior Service Costs and Actuarial Losses on Pensions and Other Postretirement Benefits1 |  | $ | 6,346 |  |  | $ | 118,433 |  |  | $ | 124,779 |  |  | see below |
Accumulated ARO Accretion/Depreciation Adjustment1 |  |  | - |  |  |  | 7,169 |  |  |  | 7,169 |  |  | asset lives |
Conservation Improvement Program Costs and Incentives2 |  |  | 5,995 |  |  |  | 3,285 |  |  |  | 9,280 |  |  |  | 21 |
Minnesota Transmission Cost Recovery Rider Accrued Revenues2 |  |  | 444 |  |  |  | - |  |  |  | 444 |  |  |  | 12 |
MISO Schedule 26/26A Transmission Cost Recovery Rider True-up1 |  |  | 240 |  |  |  | - |  |  |  | 240 |  |  |  | 12 |
Nonservice Costs Components of Postretirement Benefits Capitalized for Ratemaking Purposes and Subject to Deferred Recovery1 |  |  | - |  |  |  | 986 |  |  |  | 986 |  |  | asset lives |
Big Stone II Unrecovered Project Costs – Minnesota1 |  |  | 681 |  |  |  | 947 |  |  |  | 1,628 |  |  |  | 28 |
Debt Reacquisition Premiums1 |  |  | 207 |  |  |  | 753 |  |  |  | 960 |  |  |  | 165 |
Deferred Marked-to-Market Losses1 |  |  | 1,661 |  |  |  | 743 |  |  |  | 2,404 |  |  |  | 24 |
Big Stone II Unrecovered Project Costs – South Dakota1 |  |  | 100 |  |  |  | 342 |  |  |  | 442 |  |  |  | 53 |
South Dakota Deferred Rate Case Expenses Subject to Recovery1 |  |  | 178 |  |  |  | - |  |  |  | 178 |  |  |  | 12 |
North Dakota Deferred Rate Case Expenses Subject to Recovery1 |  |  | 455 |  |  |  | - |  |  |  | 455 |  |  |  | 12 |
Minnesota SPP Transmission Cost Recovery Tracker1 |  |  | - |  |  |  | 176 |  |  |  | 176 |  |  | see below |
Minnesota Renewable Resource Recovery Rider Accrued Revenues2 |  |  | 452 |  |  |  | - |  |  |  | 452 |  |  |  | 12 |
Minnesota Environmental Cost Recovery Rider Accrued Revenues2 |  |  | 121 |  |  |  | - |  |  |  | 121 |  |  |  | 12 |
Deferred Income Taxes1 |  |  | - |  |  |  | 2,423 |  |  |  | 2,423 |  |  | asset lives |
Minnesota Energy Intensive Trade Exposed Rider Accrued Revenues1 |  |  | 328 |  |  |  | - |  |  |  | 328 |  |  |  | 4 |
North Dakota Environmental Cost Recovery Rider Accrued Revenues2 |  |  | 17 |  |  |  | - |  |  |  | 17 |  |  |  | 12 |
Total Regulatory Assets |  | $ | 17,225 |  |  | $ | 135,257 |  |  | $ | 152,482 |  |  |  |  |
Regulatory Liabilities: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Deferred Income Taxes |  | $ | - |  |  | $ | 142,779 |  |  | $ | 142,779 |  |  | asset lives |
Accumulated Reserve for Estimated Removal Costs – Net of Salvage |  |  | - |  |  |  | 83,229 |  |  |  | 83,229 |  |  | asset lives |
Refundable Fuel Clause Adjustment Revenues |  |  | 121 |  |  |  | - |  |  |  | 121 |  |  |  | 12 |
North Dakota Renewable Resource Recovery Rider Accrued Refund |  |  | 177 |  |  |  | - |  |  |  | 177 |  |  |  | 12 |
North Dakota Transmission Cost Recovery Rider Accrued Refund |  |  | 60 |  |  |  | - |  |  |  | 60 |  |  |  | 12 |
Revenue for Rate Case Expenses Subject to Refund – Minnesota |  |  | - |  |  |  | 166 |  |  |  | 166 |  |  | see below |
MISO Schedule 26/26A Transmission Cost Recovery Rider True-up |  |  | - |  |  |  | 187 |  |  |  | 187 |  |  |  | 24 |
South Dakota Transmission Cost Recovery Rider Accrued Refund |  |  | 168 |  |  |  | - |  |  |  | 168 |  |  |  | 12 |
South Dakota Environmental Cost Recovery Rider Accrued Refund |  |  | 207 |  |  |  | - |  |  |  | 207 |  |  |  | 12 |
Other |  |  | 5 |  |  |  | 108 |  |  |  | 113 |  |  |  | 180 |
Total Regulatory Liabilities |  | $ | 738 |  |  | $ | 226,469 |  |  | $ | 227,207 |  |  |  |  |
Net Regulatory Asset/(Liability) Position |  | $ | 16,487 |  |  | $ | (91,212 | ) |  | $ | (74,725 | ) |  |  |  |

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