v3.26.1
3. Restricted Marketable Securities (Details) - Restricted Marketable Securities - USD ($)
$ in Thousands
6 Months Ended
Jun. 30, 2026
Jun. 30, 2025
Dec. 31, 2025
Debt Securities, Available-for-sale [Line Items]      
Restricted marketable securities $ 214,315   $ 217,172
Product minimum service life 25 years    
Restricted Debt Securities [Member]      
Debt Securities, Available-for-sale [Line Items]      
Restricted marketable securities $ 214,315   217,172
Payments to acquire restricted marketable securities 0 $ 5,000  
Cash Held In Trust [Member]      
Debt Securities, Available-for-sale [Line Items]      
Restricted cash and cash equivalents - noncurrent 10,500   6,900
U.S. debt [Member] | Restricted Debt Securities [Member]      
Debt Securities, Available-for-sale [Line Items]      
Restricted marketable securities 114,005   115,350
Foreign government obligations [Member] | Restricted Debt Securities [Member]      
Debt Securities, Available-for-sale [Line Items]      
Restricted marketable securities 53,321   54,156
Supranational debt [Member] | Restricted Debt Securities [Member]      
Debt Securities, Available-for-sale [Line Items]      
Restricted marketable securities 28,112   28,276
U.S. government obligations [Member] | Restricted Debt Securities [Member]      
Debt Securities, Available-for-sale [Line Items]      
Restricted marketable securities $ 18,877   $ 19,390