Investments (Details 4) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Amortized Cost
Due in less than one year, Amortized Cost	$ 270,372
Due in one to two years, Amortized Cost	161,066
Due in three to five years, Amortized Cost	44,620
Total marketable investments	476,058	857,394
Fair Value
Due in less than one year, Fair Value	270,695
Due in one to two years, Fair Value	161,356
Due in three to five years, Fair Value	44,616
Fair Value	$ 476,667	$ 857,711