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Leases Leases (Details) $ in Millions | 6 Months Ended
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Jun. 30, 2019 USD ($)
Lessee, Lease, Description [Line Items] |
Lessor, Operating Lease, Not Yet Commenced, Assumption and Judgment, Estimated Annual Operating Expense | $ 1.1
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List] | us-gaap:InvestmentsAndOtherNoncurrentAssets
Finance Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List] | us-gaap:InvestmentsAndOtherNoncurrentAssets
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List] | us-gaap:OtherLiabilitiesCurrent
Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List] | us-gaap:OtherLiabilitiesNoncurrent
Finance Lease, Liability, Current, Statement of Financial Position [Extensible List] | us-gaap:OtherLiabilitiesCurrent
Finance Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List] | us-gaap:OtherLiabilitiesNoncurrent
Minimum [Member] |
Lessee, Lease, Description [Line Items] |
Lessee, Operating Lease, Term of Contract | 1 year
Lessee, Operating Lease, Renewal Term | 5 years
Maximum [Member] |
Lessee, Lease, Description [Line Items] |
Lessee, Operating Lease, Term of Contract | 74 years
Lessee, Operating Lease, Renewal Term | 50 years
State of Montana [Member] |
Lessee, Lease, Description [Line Items] |
Lease Expiration Date | Dec. 31, 2046
Snettisham Hydroelectric Project [Member] |
Lessee, Lease, Description [Line Items] |
Lease Expiration Date | Dec. 31, 2034

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- Definition Lessor, Operating Lease, Not Yet Commenced, Assumption and Judgment, Estimated Annual Operating Expense + References No definition available. + Details
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- Definition Indicates line item in statement of financial position that includes current finance lease liability. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 842 -SubTopic 20 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=77888419&loc=SL77918631-209977 + Details
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- Definition Indicates line item in statement of financial position that includes noncurrent finance lease liability. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 842 -SubTopic 20 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=77888419&loc=SL77918631-209977 + Details
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- Definition Indicates line item in statement of financial position that includes finance lease right-of-use asset. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 842 -SubTopic 20 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=77888419&loc=SL77918631-209977 + Details
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- Definition Date which lease or group of leases is set to expire, in CCYY-MM-DD format. + References No definition available. + 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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- Definition Term of lessee's operating lease renewal, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 842 -SubTopic 20 -Section 50 -Paragraph 3 -Subparagraph (a)(3) -URI http://asc.fasb.org/extlink&oid=77888426&loc=SL77918673-209980 + Details
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- Definition Term of lessee's operating lease, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 842 -SubTopic 20 -Section 50 -Paragraph 3 -Subparagraph (a)(3) -URI http://asc.fasb.org/extlink&oid=77888426&loc=SL77918673-209980 + Details
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