FAIR VALUE MEASUREMENTS (Tables)
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6 Months Ended |
Jun. 30, 2026 |
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| Fair Value Disclosures [Abstract] |
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| Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis |
The carrying amounts and estimated fair values by input level of the Company’s financial instruments were as follows: | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | June 30, 2026 | | (in thousands) | Carrying Amount | | Fair Value | | Level 1 | | Level 2 | | Level 3 | | Financial assets: | | | | | | | | | | | Cash and cash equivalents | $ | 429,075 | | | $ | 429,075 | | | $ | 429,075 | | | $ | — | | | $ | — | | | Short-term investments | $ | 1,023,564 | | | $ | 1,023,564 | | | $ | 1,023,564 | | | $ | — | | | $ | — | | | Restricted cash | $ | 541 | | | $ | 541 | | | $ | 541 | | | $ | — | | | $ | — | | Derivative instrument | $ | 11,583 | | | $ | 11,583 | | | $ | — | | | $ | — | | | $ | 11,583 | | | Financial liabilities: | | | | | | | | | | | | | | | | | | | | 2030 Notes | $ | 847,267 | | | $ | 2,314,641 | | | $ | 2,314,641 | | | $ | — | | | $ | — | | Samarium Project Loan | $ | 87,316 | | | $ | 98,536 | | | $ | — | | | $ | 98,536 | | | $ | — | | | Equipment notes | $ | 29,099 | | | $ | 29,972 | | | $ | — | | | $ | 29,972 | | | $ | — | |
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | December 31, 2025 | | (in thousands) | Carrying Amount | | Fair Value | | Level 1 | | Level 2 | | Level 3 | | Financial assets: | | | | | | | | | | | Cash and cash equivalents | $ | 1,166,011 | | | $ | 1,166,011 | | | $ | 1,166,011 | | | $ | — | | | $ | — | | | Short-term investments | $ | 664,275 | | | $ | 664,275 | | | $ | 664,275 | | | $ | — | | | $ | — | | | Restricted cash | $ | 1,348 | | | $ | 1,348 | | | $ | 1,348 | | | $ | — | | | $ | — | | | Derivative instrument | $ | 8,708 | | | $ | 8,708 | | | $ | — | | | $ | — | | | $ | 8,708 | | | Financial liabilities: | | | | | | | | | | 2026 Notes | $ | 67,411 | | | $ | 82,449 | | | $ | 82,449 | | | $ | — | | | $ | — | | 2030 Notes | $ | 845,301 | | | $ | 2,172,782 | | | $ | 2,172,782 | | | $ | — | | | $ | — | | | Samarium Project Loan | $ | 86,029 | | | $ | 98,081 | | | $ | — | | | $ | 98,081 | | | $ | — | | | Equipment notes | $ | 24,270 | | | $ | 25,339 | | | $ | — | | | $ | 25,339 | | | $ | — | |
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| Fair Value Disclosure of Asset and Liability Not Measured at Fair Value |
The carrying amounts and estimated fair values by input level of the Company’s financial instruments were as follows: | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | June 30, 2026 | | (in thousands) | Carrying Amount | | Fair Value | | Level 1 | | Level 2 | | Level 3 | | Financial assets: | | | | | | | | | | | Cash and cash equivalents | $ | 429,075 | | | $ | 429,075 | | | $ | 429,075 | | | $ | — | | | $ | — | | | Short-term investments | $ | 1,023,564 | | | $ | 1,023,564 | | | $ | 1,023,564 | | | $ | — | | | $ | — | | | Restricted cash | $ | 541 | | | $ | 541 | | | $ | 541 | | | $ | — | | | $ | — | | Derivative instrument | $ | 11,583 | | | $ | 11,583 | | | $ | — | | | $ | — | | | $ | 11,583 | | | Financial liabilities: | | | | | | | | | | | | | | | | | | | | 2030 Notes | $ | 847,267 | | | $ | 2,314,641 | | | $ | 2,314,641 | | | $ | — | | | $ | — | | Samarium Project Loan | $ | 87,316 | | | $ | 98,536 | | | $ | — | | | $ | 98,536 | | | $ | — | | | Equipment notes | $ | 29,099 | | | $ | 29,972 | | | $ | — | | | $ | 29,972 | | | $ | — | |
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | December 31, 2025 | | (in thousands) | Carrying Amount | | Fair Value | | Level 1 | | Level 2 | | Level 3 | | Financial assets: | | | | | | | | | | | Cash and cash equivalents | $ | 1,166,011 | | | $ | 1,166,011 | | | $ | 1,166,011 | | | $ | — | | | $ | — | | | Short-term investments | $ | 664,275 | | | $ | 664,275 | | | $ | 664,275 | | | $ | — | | | $ | — | | | Restricted cash | $ | 1,348 | | | $ | 1,348 | | | $ | 1,348 | | | $ | — | | | $ | — | | | Derivative instrument | $ | 8,708 | | | $ | 8,708 | | | $ | — | | | $ | — | | | $ | 8,708 | | | Financial liabilities: | | | | | | | | | | 2026 Notes | $ | 67,411 | | | $ | 82,449 | | | $ | 82,449 | | | $ | — | | | $ | — | | 2030 Notes | $ | 845,301 | | | $ | 2,172,782 | | | $ | 2,172,782 | | | $ | — | | | $ | — | | | Samarium Project Loan | $ | 86,029 | | | $ | 98,081 | | | $ | — | | | $ | 98,081 | | | $ | — | | | Equipment notes | $ | 24,270 | | | $ | 25,339 | | | $ | — | | | $ | 25,339 | | | $ | — | |
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| Fair Value Measurement Inputs and Valuation Techniques |
The following assumptions were used within the model: | | | | | | | | | | | | | | | Valuation Assumptions: | | June 30, 2026 | | December 31, 2025 | Expected volatility | | 76.2 | % | | 79.6 | % | Risk-free interest rate | | 4.2 | % | | 3.7 | % | Discount rate | | 8.2 | % | | 7.7 | % | Dividend yield | | — | % | | — | % | Term to maturity | | 3.7 years | | 4.2 years | Stock price | | $ | 56.01 | | $ | 50.52 |
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| Schedule of Derivative Assets at Fair Value |
The following table summarizes the changes in fair value of the Company’s Level 3 assets measured on a recurring basis: | | | | | | | | | | | | | | | | | | | | | | | | | For the three months ended June 30, | | For the six months ended June 30, | (in thousands) | 2026 | | 2025 | | 2026 | | 2025 | Beginning balance | $ | 12,806 | | | $ | 6,997 | | | $ | 8,708 | | | $ | — | | Included in earnings(1) | (1,223) | | | (2,529) | | | 2,875 | | | 4,468 | | Ending balance | $ | 11,583 | | | $ | 4,468 | | | $ | 11,583 | | | $ | 4,468 | |
(1)The gains (losses) are included in “Other income, net” within the Company’s unaudited Condensed Consolidated Statements of Operations.
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