Financial Instruments (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Cash	$ 27,162	$ 33,238
Time deposits	4,078	3,924
Money Market Funds (level 1)	123,869	149,624
Financial Instruments, Owned, US Government and Agency Obligations, at Fair Value	1,004,658	1,040,678
Total	1,159,767	1,227,464
Included in Cash and cash equivalents	145,701	508,196
Restricted Cash Equivalents, Noncurrent	9,408	9,405
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	155,109	517,601	$ 118,679	$ 366,753
Included in Marketable securities	$ 1,004,658	$ 709,863

Amount of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes 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. Excludes cash and cash equivalents within disposal group and discontinued operation.

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Amount of investment in marketable security, classified as current.

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Investment in short-term money-market instruments (such as commercial paper, banker's acceptances, repurchase agreements, government securities, certificates of deposit, and so forth) which are highly liquid (that is, readily convertible to known amounts of cash) and so near their maturity that they present an insignificant risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify as cash equivalents by definition. Original maturity means an 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.

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