Commitments and Contingencies	6 Months Ended
Commitments and Contingencies	Jun. 30, 2023
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies Retention Agreements As of December 31, 2022, the Company had an outstanding liability of $1.4 million (the "Retention Liability"), which was included in the "Other current liabilities" line item in the Condensed Consolidated Balance Sheet, related to retention agreements (the "Retention Agreements") executed between the Company and its executive officers and certain other key employees in May 2021 and amended in May 2022 in order to maintain the Company's business operations while it pursued and executed on its strategic initiatives. The Retention Agreements were approved by the Compensation Committee of the Board of Directors and the Board of Directors (the "Board") in May 2021 and May 2022. In August 2022, the Company paid $1.0 million pursuant to the payment terms of the Retention Agreements and the Retention Liability was paid in full in January 2023. Surety Bonds and Restricted Cash As the owner of the Five Forks Mine, the Company is required to post a surety bond with a regulatory commission. As of June 30, 2023 and December 31, 2022, the Company had posted a $7.5 million surety bond related to performance requirements associated with the Five Forks Mine. The Company leases land adjacent to the Corbin Facility and is required to post surety bonds with a regulatory commission for reclamation. As of June 30, 2023, the amount of these surety bonds was $3.0 million. The Company holds permits for an abandoned mine in West Virginia ("Mine 4") and is required to post a surety bond with a regulatory commission for reclamation. As of June 30, 2023, the amount of this surety bond was $0.7 million. As the owner of the Marshall Mine, the Company was required to post a surety bond with a regulatory commission. As of December 31, 2022, the Company posted a $16.6 million surety bond that was released upon all of the Conditions for closing the MM Transaction being satisfied, which occurred on March 27, 2023. As of June 30, 2023 and December 31, 2022, the Company posted cash collateral of $8.6 million and $10.0 million, respectively, as required by the Company's surety bond providers, which is reported as long-term restricted cash in the Condensed Consolidated Balance Sheets. As of June 30, 2023, the Company holds a deposit of $0.4 million with a third party for collateral as required under a bonding arrangement for Mine 4. This deposit is included in "Other long-term assets, net" in the Condensed Consolidated Balance Sheet as of June 30, 2023. Tinuum Group In addition to those obligations described in Note 10, the Company has certain limited obligations contingent upon future events in connection with the activities of Tinuum Group. The Company, NexGen Refined Coal, LLC ("NexGen") and two entities affiliated with NexGen have provided an affiliate of the Goldman Sachs Group, Inc. with limited guaranties (the "Tinuum Group Party Guaranties") related to certain losses it may suffer as a result of inaccuracies or breach of representations and covenants committed by Tinuum Group. The Company also is a party to a contribution agreement with NexGen under which any party called upon to pay on a Tinuum Group Party Guaranty is entitled to receive contributions from the other party equal to 50% of the amount paid. The Company has not recorded a liability or expense provision related to this contingent obligation as it believes that it is not probable that a loss will occur with respect to the Tinuum Group Party Guaranties. Legal Proceedings The Company is from time to time subject to various pending or threatened legal actions and proceedings, including those that arise in the ordinary course of its business. Such matters are subject to many uncertainties and outcomes, the financial impacts of which are not predictable with assurance and that may not be known for extended periods of time. The Company records a liability in its consolidated financial statements for costs related to claims, settlements and judgments where management has assessed that a loss is probable and an amount can be reasonably estimated. There were no significant legal proceedings as of June 30, 2023.