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3. Restricted Marketable Securities (Details) - Restricted Marketable Securities - USD ($)
$ in Thousands
9 Months Ended
Sep. 30, 2024
Dec. 31, 2023
Debt Securities, Available-for-sale [Line Items]    
Restricted marketable securities $ 211,130 $ 198,310
Product minimum service life 25 years  
Restricted Debt Securities [Member]    
Debt Securities, Available-for-sale [Line Items]    
Restricted marketable securities $ 211,130 198,310
Payments to acquire restricted marketable securities 7,900  
Cash Held In Trust [Member]    
Debt Securities, Available-for-sale [Line Items]    
Restricted cash and cash equivalents - noncurrent 4,500 6,200
Foreign government obligations [Member] | Restricted Debt Securities [Member]    
Debt Securities, Available-for-sale [Line Items]    
Restricted marketable securities 52,368 51,229
Supranational debt [Member] | Restricted Debt Securities [Member]    
Debt Securities, Available-for-sale [Line Items]    
Restricted marketable securities 23,350 15,339
U.S. debt [Member] | Restricted Debt Securities [Member]    
Debt Securities, Available-for-sale [Line Items]    
Restricted marketable securities 116,157 113,326
U.S. government obligations [Member] | Restricted Debt Securities [Member]    
Debt Securities, Available-for-sale [Line Items]    
Restricted marketable securities $ 19,255 $ 18,416