Commitments and Contingencies (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2022	Sep. 30, 2022	Dec. 31, 2021
Loss Contingencies [Line Items]
Surety Bonds Outstanding	$ 583,600	$ 583,600
Letters of credit outstanding	95,400	95,400
Cash collateral for surety bond	5,600	5,600
Contribution to fund asset retirement obligations		110,000
Long-term asset retirement obligation	130,000	130,000	$ 20,000
Asset retirement obligations
Loss Contingencies [Line Items]
Reclamation-related obligations	217,400	217,400
Surety Bonds Outstanding	494,800	494,800
Letters of credit outstanding	20,000	20,000
Cash collateral for surety bond	600	600
Contribution to fund asset retirement obligations	30,000
Long-term asset retirement obligation	$ 130,000	$ 130,000

The amount contributed to sinking fund for asset retirement obligation.

No definition available.

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Period Type:	duration

- Definition

The carrying amount held in sinking fund for long term asset retirement obligation as at the end of the reporting period.

+ References

No definition available.

+ Details

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Namespace Prefix:	arch_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Surety bonds outstanding to cover future obligations.

+ References

No definition available.

+ Details

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- Definition

Noncurrent portion of 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

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)
-URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849

+ Details

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- Definition

Carrying value of amounts transferred to third parties for security purposes that are expected to be returned or applied towards payment after one year or beyond the operating cycle, if longer.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.17)
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

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- Definition

The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

+ 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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- Details

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