Commitments and Contingencies - Cash Deposits Held by Third Parties (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Long-term Purchase Commitment [Line Items]
Total deposits	$ 21,079	$ 10,723
Reclamation-related obligations
Long-term Purchase Commitment [Line Items]
Total deposits	19,660	8,887
Other operating agreements
Long-term Purchase Commitment [Line Items]
Total deposits	$ 1,419	$ 1,836

The carrying amount of the asset transferred to a third party to serve as a deposit, which typically serves as security against failure by the transferor to perform under terms of an agreement.

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 210.5-02.8,17)
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

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