v3.25.2
3. Restricted Marketable Securities (Details) - Restricted Marketable Securities - USD ($)
$ in Thousands
6 Months Ended
Jun. 30, 2025
Jun. 30, 2024
Dec. 31, 2024
Debt Securities, Available-for-sale [Line Items]      
Restricted marketable securities $ 213,737   $ 199,136
Product minimum service life 25 years    
Restricted Debt Securities [Member]      
Debt Securities, Available-for-sale [Line Items]      
Restricted marketable securities $ 213,737   199,136
Payments to acquire restricted marketable securities 5,000 $ 7,900  
Cash Held In Trust [Member]      
Debt Securities, Available-for-sale [Line Items]      
Restricted cash and cash equivalents - noncurrent 3,500   5,000
U.S. debt [Member] | Restricted Debt Securities [Member]      
Debt Securities, Available-for-sale [Line Items]      
Restricted marketable securities 112,855   109,155
Foreign government obligations [Member] | Restricted Debt Securities [Member]      
Debt Securities, Available-for-sale [Line Items]      
Restricted marketable securities 53,942   49,024
Supranational debt [Member] | Restricted Debt Securities [Member]      
Debt Securities, Available-for-sale [Line Items]      
Restricted marketable securities 28,100   22,809
U.S. government obligations [Member] | Restricted Debt Securities [Member]      
Debt Securities, Available-for-sale [Line Items]      
Restricted marketable securities $ 18,840   $ 18,148