Investment valuation (Details) - US Government Debt Securities [Member] - USD ($) $ in Thousands	Sep. 30, 2022	Dec. 31, 2021
Investment valuation (Details) [Line Items]
Investments in U.S. Treasury bills	$ 2,421,000
U.S. Treasury bills included in cash and cash equivalents		$ 5,250,000

Debt securities issued by a United States government agency such as Government National Mortgage Association (Ginnie Mae), Federal Home Loan Mortgage Corporation (Freddie Mac), and Federal National Mortgage Association (Fannie Mae), which are short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify under that definition. Original maturity means original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three-years ago does not become a cash equivalent when its remaining maturity is three months.

No definition available.

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