3. Restricted Marketable Securities (Details) - Restricted Marketable Securities - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Dec. 31, 2023
Debt Securities, Available-for-sale [Line Items]
Restricted marketable securities	$ 194,482	$ 198,310
Product minimum service life	25 years
Restricted Debt Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Restricted marketable securities	$ 194,482	198,310
Cash Held In Trust [Member]
Debt Securities, Available-for-sale [Line Items]
Restricted cash and cash equivalents - noncurrent	9,000	6,200
Foreign government obligations [Member] | Restricted Debt Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Restricted marketable securities	49,894	51,229
Supranational debt [Member] | Restricted Debt Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Restricted marketable securities	15,110	15,339
U.S. debt [Member] | Restricted Debt Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Restricted marketable securities	110,826	113,326
U.S. government obligations [Member] | Restricted Debt Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Restricted marketable securities	$ 18,652	$ 18,416