SEGMENT AND RELATED INFORMATION: - Receivables (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Financial information related to segments
Trade receivables	$ 1,068.9	$ 832.9	$ 822.4
Related parties receivable current:	23.3	30.0	101.5
Related parties receivable non-current:		59.5
Corporate, other and eliminations
Financial information related to segments
Related parties receivable current:	7.1	7.9	19.9
Mexican Open-pit
Financial information related to segments
Trade receivables	566.0	477.8	505.9
Related parties receivable current:	15.4	22.1	81.6
Related parties receivable non-current:		59.5
Mexican IMMSA Unit
Financial information related to segments
Trade receivables	57.8	38.0	50.5
Peruvian Operations
Financial information related to segments
Trade receivables	445.1	$ 317.1	$ 266.0
Related parties receivable current:	$ 0.8

The aggregate amount of receivables to be collected from related parties where one party can exercise control or significant influence over another party; including affiliates, owners or officers and their immediate families, pension trusts, and so forth, at the financial statement date. which are usually due within one year (or one business cycle).

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(k)(1))
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
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-Subparagraph (SX 210.5-02(11))
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 850
-SubTopic 10
-Section 50
-Paragraph 1
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-URI http://asc.fasb.org/extlink&oid=6457730&loc=d3e39549-107864

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
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-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
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-URI http://asc.fasb.org/extlink&oid=121566466&loc=d3e6676-107765

Name:	us-gaap_DueFromRelatedPartiesCurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant