Investments (Details 4) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Amortized Cost
Due in less than one year, Amortized Cost	$ 121,974
Due in one to two years, Amortized Cost	38,002
Total marketable investments	159,976	$ 420,500
Fair Value
Due in less than one year, Fair Value	121,932
Due in one to two years, Fair Value	37,898
Fair Value	$ 159,830	$ 420,731