ASSET RETIREMENT OBLIGATION: (Details) $ in Millions	9 Months Ended	12 Months Ended
Sep. 30, 2020 USD ($) item	Sep. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)
ASSET RETIREMENT OBLIGATION:
Maximum annual guarantees secured	50.00%
Percentage of guarantee for Lima complex	50.00%
Percentage of security for LOC	50.00%
Total guarantees	$ 47.1
Asset retirement obligation activity
Balance at the beginning of the year	262.3	$ 217.7	$ 217.7
Changes in estimates		25.2
Closure Payments	(1.0)	(0.8)
Accretion expense	11.1	9.5
Balance at the end of the year	$ 272.4	$ 251.6	262.3
Peru
ASSET RETIREMENT OBLIGATION:
Period after which successive reviews are required by the law (in years)	5 years
Number of units with future closure costs recognized as an asset retirement obligation \| item	3
Asset retirement obligation activity
Changes in estimates			$ 28.1

Represents the period after which successive reviews are required by the law.

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- Definition

Represents the number of units for which the entity has recognized an asset retirement obligation.

+ References

No definition available.

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- Definition

Maximum percentage of annual guarantees secured.

+ References

No definition available.

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- Definition

Percentage of guarantee pledged for office complex.

+ References

No definition available.

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- Definition

Percentage of guarantee for stand by letters of credit.

+ References

No definition available.

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- Definition

The carrying amount of a liability for an asset retirement obligation. An asset retirement obligation is a legal obligation associated with the disposal or retirement of a tangible long-lived asset that results from the acquisition, construction or development, or the normal operations of a long-lived asset, except for certain obligations of lessees.

+ References

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- References

No definition available.

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- Definition

Amount of accretion expense recognized during the period that is associated with an asset retirement obligation. Accretion expense measures and incorporates changes due to the passage of time into the carrying amount of the liability.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 410
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (c)(3)
-URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 410
-SubTopic 20
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6392676&loc=d3e7480-110848

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- Definition

Amount of asset retirement obligations settled, or otherwise disposed of, during the period. This may include asset retirement obligations transferred to third parties associated with the sale of a long-lived asset.

+ References

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- Definition

Amount of increase (decrease) in the asset retirement obligation from changes in the amount or timing of the estimated cash flows associated with the settlement of the obligation.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 410
-SubTopic 20
-Section 35
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=6392603&loc=d3e7123-110846

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
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-Paragraph 1
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-URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849

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- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

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- Definition

Maximum potential amount of future payments (undiscounted) the guarantor could be required to make under the guarantee or each group of similar guarantees before reduction for potential recoveries under recourse or collateralization provisions.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 460
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph (b)(1)
-URI http://asc.fasb.org/extlink&oid=121555522&loc=d3e12069-110248

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