Financial Instruments (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Cash	$ 135,092	$ 39,183
Money market funds	3,682	4,632
Time deposits	116,068	134,790
Available-for-sale Securities, Debt Maturities, Next Twelve Months, Fair Value	2,169,172	1,626,764
Available-for-sale Securities, Equity Securities	25	2,174
Total	2,424,039	1,807,543
Included in Cash and cash equivalents	465,851	231,945	$ 228,659	$ 191,608
Included in Marketable securities	1,948,900	1,565,962
Included in Other assets (Restricted cash)	$ 9,288	$ 9,636

Fair value of available-for-sale debt securities maturing in the next fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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