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Note 14 - Income Taxes (Details Textual) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent | 21.00% | 21.00% | 35.00%
Increase (Decrease) in Percentage of Production Tax Credits |  | (53.00%) |
Wind Tax Credits, Amortization Period |  | 25 years |
Period for Unrecognized Tax Benefits Not Expected Change | 12 months |  |
Unrecognized Tax Benefits, Interest on Income Taxes Accrued | $ 0 |  |
Income Tax Expense (Benefit), Continuing Operations, Adjustment of Deferred Tax (Asset) Liability | $ 0 | $ 0 | $ 1,756
Domestic Tax Authority [Member] |  |  |
Open Tax Year | 2016 2017 2018 2019 |  |
State and Local Jurisdiction [Member] | Minnesota Department of Revenue [Member] |  |  |
Open Tax Year | 2015 2016 2017 2018 2019 |  |
State and Local Jurisdiction [Member] | North Dakota Department of Revenue [Member] |  |  |
Open Tax Year | 2016 2017 2018 2019 |  |

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- Definition Represents the increase (decrease) in the percentage of production tax credits during the period. + References No definition available. + Details
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- Definition Percentage of domestic federal statutory tax rate applicable to pretax income (loss). + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SAB TOPIC 6.I) -URI http://asc.fasb.org/extlink&oid=116825942&loc=d3e330036-122817 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 12 -URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32687-109319 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 13 -URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32698-109319 + Details
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- Definition Amount of income tax expense (benefit) from continuing operations attributable to an adjustment of a deferred tax liability or asset for enacted changes in tax laws or rates or a change in the tax status of the entity. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 9 -Subparagraph (g) -URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32639-109319 + Details
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- Definition Tax year that remains open to examination under enacted tax laws, in CCYY format. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 15 -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32718-109319 + Details
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- Definition Amount of interest expense accrued for an underpayment of income taxes. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 15 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32718-109319 + Details
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