Fair Value of Financial Instruments (Details 4) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Fair Value of Financial Instruments
Corporate debt securities, Amortized Cost	$ 57,967	$ 48,259
Corporate debt securities, Gross Unrealized Gains	33	1
Corporate debt securities, Gross Unrealized Losses	(33)	(54)
Corporate debt securities, Fair Value	57,967	48,206
Contractual maturities of the unrestricted marketable securities held
Less Than 1 Year	49,211
1-5 years	8,756
Corporate debt securities, Fair Value	$ 57,967	$ 48,206