Summary of Significant Accounting Policies (Details 4) $ in Thousands	Sep. 30, 2015 USD ($) item	Dec. 31, 2014 USD ($) item
Unrealized loss position for less than one year
Number of marketable securities in an unrealized loss position for less than one year | item	52	44
Number of marketable securities in an unrealized loss position for greater than one year | item	0	1
Corporate debt securities | Due in one year or less
Unrealized loss position for less than one year
Aggregate Fair Value	$ 89,793	$ 63,221
Unrealized Losses	(116)	(24)
Foreign government bonds | Due in one year or less
Unrealized loss position for less than one year
Aggregate Fair Value		12,773
Unrealized Losses		(1)
Asset-backed securities | Due in one year or less
Unrealized loss position for less than one year
Aggregate Fair Value	52,558	25,742
Unrealized Losses	$ (12)	$ (9)