Financial Instruments (Details 2) $ in Thousands	Dec. 31, 2016 USD ($)
Amortized cost and estimated fair value of marketable debt securities
Amortized Cost Due in one year or less	$ 839,365
Amortized Cost Due after one year through five years	496,399
Amortized Cost Due after five years through ten years	243,772
Amortized Cost Due after ten years	1,358,644
Amortized Cost Total	2,938,180
Estimated Fair Value Due in one year or less	839,380
Estimated Fair Value Due after one year through five years	494,352
Estimated Fair Value Due after five years through ten years	243,648
Estimated Fair Value Due after ten years	1,345,190
Estimated Fair Value Total	2,922,570
Marketable debt securities with contractual maturities greater than one year but classified as short-term investment	$ 1,950,000