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Jointly owned facilities (Details) - USD ($) $ in Thousands | Dec. 31, 2016 | Dec. 31, 2015
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Big Stone Station: |  |
Jointly owned facilities [Line Items] |  |
Utility plant in service | $ 157,144 | $ 157,761
Less accumulated depreciation | 49,568 | 48,242
Utility plant in services net | 107,576 | 109,519
Coyote Station: |  |
Jointly owned facilities [Line Items] |  |
Utility plant in service | 156,334 | 140,895
Less accumulated depreciation | 105,928 | 94,755
Utility plant in services net | 50,406 | 46,140
Wygen III: |  |
Jointly owned facilities [Line Items] |  |
Utility plant in service | 66,251 | 65,023
Less accumulated depreciation | 7,550 | 6,788
Utility plant in services net | $ 58,701 | $ 58,235

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- Definition The period end amount owned by the reporting utility of a jointly owned utility plant in service. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 360 -Section S99 -Paragraph 1 -Subparagraph (SAB Topic 10.C) -URI http://asc.fasb.org/extlink&oid=6500719&loc=d3e659983-123033 + Details
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- Definition The total period end amount of plant in service and construction in progress net of accumulated depreciation for the utility's share of jointly owned electricity generation plant. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 360 -Section S99 -Paragraph 1 -Subparagraph (SAB Topic 10.C) -URI http://asc.fasb.org/extlink&oid=6500719&loc=d3e659983-123033 + Details
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- Definition The period end amount of accumulated depreciation in a jointly owned electricity generation plant. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 360 -Section S99 -Paragraph 1 -Subparagraph (SAB Topic 10.C) -URI http://asc.fasb.org/extlink&oid=6500719&loc=d3e659983-123033 + Details
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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- Details
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