Fair Value of Financial Instruments (Details 4) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Fair Value of Financial Instruments
Corporate debt securities, Amortized Cost	$ 75,482	$ 57,910
Corporate debt securities, Gross Unrealized Gains	23	4
Corporate debt securities, Gross Unrealized Losses	(130)	(158)
Corporate debt securities, Fair Value	75,375	57,756
Contractual maturities of the unrestricted marketable securities held
Less Than 1 Year	31,408
1-5 years	43,967
Corporate debt securities, Fair Value	$ 75,375	$ 57,756