Financial Instruments (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016	Sep. 30, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Cash	$ 33,466	$ 39,183
Time deposits	3,139	4,632
Total	2,375,009	1,807,543
Included in Cash and cash equivalents	286,822	231,945	$ 177,785	$ 228,659
Included in Marketable securities	2,078,905	1,565,962
Included in Other assets (Restricted cash)	9,282	9,636
Fair Value, Inputs, Level 1 [Member]
Schedule of Available-for-sale Securities [Line Items]
Money Market Funds (level 1)	259,499	134,790
Financial Instruments, Owned, US Government and Agency Obligations, at Fair Value	2,078,882	1,626,764
Equity Securities of Public Companies	$ 23	$ 2,174

Amount of equity securities categorized neither as held-to-maturity nor as trading.

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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 investments in debt and equity securities, including, but not limited to, held-to-maturity, trading and available-for-sale expected to be converted to cash, sold or exchanged within one year or the normal operating cycle, if longer.

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