Financial Instruments (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2017
Debt Securities, Available-for-sale [Line Items]
Cash	$ 26,141	$ 37,190
Time deposits	4,481	3,810
Money Market Funds (level 1)	271,146	120,832
Financial Instruments, Owned, US Government and Agency Obligations, at Fair Value	960,577	1,117,175
Total	1,262,345	1,279,007
Included in Cash and cash equivalents	779,625	357,415
Restricted Cash Equivalents, Noncurrent	9,355	9,338
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	788,980	366,753	$ 1,713,017	$ 475,139
Included in Marketable securities	$ 473,365	$ 912,254

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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