Contract Obligations (Schedule of Contract Obligations) (Details) - USD ($) $ in Thousands |
Jun. 30, 2025 |
Dec. 31, 2024 |
|---|---|---|
| Contract Obligations [Line Items] | ||
| Contract obligations, Current | $ 21,983 | $ 37,090 |
| Contract obligations, Non-current | 448,987 | 312,822 |
| Deferred consideration liability | 319,082 | 285,050 |
| Coal Leases Contract Liability [Member] | ||
| Contract Obligations [Line Items] | ||
| Contract obligations, Current | 843 | 843 |
| Contract obligations, Non-current | 18,981 | 19,156 |
| Stanwell Below Market Coal Supply Agreement [Member] | ||
| Contract Obligations [Line Items] | ||
| Contract obligations, Current | 21,140 | 36,247 |
| Contract obligations, Non-current | 13,101 | 8,616 |
| Prepaid Coal Supply Liability - Stanwell [Member] | ||
| Contract Obligations [Line Items] | ||
| Contract obligations | $ 97,823 | $ 0 |