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LEASES - Summary of other information related to leases (Details) - USD ($) $ in Millions | 3 Months Ended
--- | ---
Mar. 31, 2020 | Mar. 31, 2019
Business Acquisition [Line Items] |  |  |
Operating leases within cash flows from operating activities |  | $ 1.1 | $ 1.0
Finance leases within cash flows from operating activities |  | 0.5 | 0.3
Finance leases within cash flows from financing activities |  | 2.1 | 0.8
Right-of-use assets obtained in exchange for new finance lease liabilities1 | [1] | $ 29.9 | $ 15.1
Weighted-average remaining lease term - operating leases (in years) |  | 8 years | 10 years
Weighted-average remaining lease term - finance leases (in years) |  | 11 years | 6 years
Weighted-average discount rate - operating leases |  | 8.40% | 7.90%
Weighted-average discount rate - finance leases |  | 6.80% | 4.70%
AK Steel Holding Corporation [Member] |  |  |
Business Acquisition [Line Items] |  |  |
Right-of-use assets obtained in exchange for new finance lease liabilities1 |  | $ 5.3 |
[1] | 1 Does not include right-of-use assets obtained in the Merger of $5.3 million for the three months ended March 31, 2020.

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- Definition Amount of interest paid on finance lease liability. + References Reference 1: 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=77888426&loc=SL77918686-209980 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 842 -SubTopic 20 -Section 45 -Paragraph 5 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=77888419&loc=SL77918643-209977 + Details
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- Definition Amount of cash outflow for principal payment on finance lease. + 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 (a) -URI http://asc.fasb.org/extlink&oid=77888419&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=77888426&loc=SL77918686-209980 + Details
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- Definition Weighted average remaining lease term for finance 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/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=77888426&loc=SL77918686-209980 Reference 2: 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=77888399&loc=SL77918982-209971 + Details
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