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Operations and Significant Accounting Policies - Leases (Details) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2021 | Dec. 31, 2020
Lessee, Lease, Description [Line Items] |  |
Lessee, Operating Lease, Residual Value Guarantee, Description | Our largest operating lease is for the dragline at BNI Energy which includes a termination payment at the end of the lease term if we do not exercise our purchase option. |
Operating Lease, Right-of-Use Asset | $ 16.4 | $ 22.4
Operating Lease, Cost | 6.7 | 8.3
Operating Lease, Payments | 6.7 | $ 8.3
Operating Lease Liabilities, Current | 4.8 |
Operating Lease Liabilities, Non-Current | 11.6 |
Operating Lease, Liability | 16.4 |
Residual Value of Leased Asset | $ 3.0 |
Operating Lease, Liability, Current, Statement of Financial Position [Extensible Enumeration] | Other | Other
Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible Enumeration] | Other Non-Current Liabilities | Other Non-Current Liabilities
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible Enumeration] | Other Non-Current Assets | Other Non-Current Assets
Other Liabilities |  |
Lessee, Lease, Description [Line Items] |  |
Operating Lease, Liability | $ 16.4 | $ 22.4
Other Noncurrent Liabilities |  |
Lessee, Lease, Description [Line Items] |  |
Operating Lease Liabilities, Non-Current | 11.6 | 16.5
Other Current Liabilities |  |
Lessee, Lease, Description [Line Items] |  |
Operating Lease Liabilities, Current | $ 4.8 | $ 5.9
Vehicles and Equipment [Member] |  |
Lessee, Lease, Description [Line Items] |  |
Operating Lease, Weighted Average Remaining Lease Term | 3 years | 3 years
Operating Lease, Weighted Average Discount Rate, Percent | 3.80% | 3.10%
Land and Other [Member] |  |
Lessee, Lease, Description [Line Items] |  |
Operating Lease, Weighted Average Remaining Lease Term | 27 years | 27 years
Operating Lease, Weighted Average Discount Rate, Percent | 4.50% | 4.10%

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- Definition Description of terms and conditions of residual value guarantee provided by lessee on operating lease. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 842 -SubTopic 20 -Section 50 -Paragraph 3 -Subparagraph (a)(4) -URI http://asc.fasb.org/extlink&oid=123408670&loc=SL77918673-209980 + Details
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- Definition Amount of single lease cost, calculated by allocation of remaining cost of lease over remaining lease term. Includes, but is not limited to, single lease cost, after impairment of right-of-use asset, calculated by amortization of remaining right-of-use asset and accretion of lease liability. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 842 -SubTopic 20 -Section 55 -Paragraph 53 -URI http://asc.fasb.org/extlink&oid=123414884&loc=SL77918982-209971 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 842 -SubTopic 20 -Section 50 -Paragraph 4 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=123408670&loc=SL77918686-209980 + Details
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- Definition Present value of lessee's discounted obligation for lease payments from operating lease. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 842 -SubTopic 20 -Section 45 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=123391704&loc=SL77918627-209977 + Details
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- Definition Present value of lessee's discounted obligation for lease payments from operating lease, classified as current. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 842 -SubTopic 20 -Section 45 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=123391704&loc=SL77918627-209977 + Details
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- Definition Amount of cash outflow from operating lease, excluding payments to bring another asset to condition and location necessary for its intended use. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 842 -SubTopic 20 -Section 45 -Paragraph 5 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=123391704&loc=SL77918643-209977 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 842 -SubTopic 20 -Section 50 -Paragraph 4 -Subparagraph (g)(1) -URI http://asc.fasb.org/extlink&oid=123408670&loc=SL77918686-209980 + Details
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- Definition Amount of lessee's right to use underlying asset under operating lease. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 842 -SubTopic 20 -Section 45 -Paragraph 1 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=123391704&loc=SL77918627-209977 + Details
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- Definition Weighted average remaining lease term for 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/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 842 -SubTopic 20 -Section 55 -Paragraph 53 -URI http://asc.fasb.org/extlink&oid=123414884&loc=SL77918982-209971 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 842 -SubTopic 20 -Section 50 -Paragraph 4 -Subparagraph (g)(3) -URI http://asc.fasb.org/extlink&oid=123408670&loc=SL77918686-209980 + Details
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