Fair Value of Financial Instruments (Details 3) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014 Fair Value	Dec. 31, 2013 Fair Value	Jun. 30, 2014 Fair Value Certificates of deposit	Dec. 31, 2013 Fair Value Certificates of deposit	Jun. 30, 2014 Fair Value Corporate notes	Dec. 31, 2013 Fair Value Corporate notes	Jun. 30, 2014 Fair Value U.S. government debt securities	Dec. 31, 2013 Fair Value U.S. government debt securities	Jun. 30, 2014 Level 1	Dec. 31, 2013 Level 1	Jun. 30, 2014 Level 2	Dec. 31, 2013 Level 2	Jun. 30, 2014 Level 2 Certificates of deposit	Dec. 31, 2013 Level 2 Certificates of deposit	Jun. 30, 2014 Level 2 Corporate notes	Dec. 31, 2013 Level 2 Corporate notes	Jun. 30, 2014 Level 2 U.S. government debt securities	Dec. 31, 2013 Level 2 U.S. government debt securities
Fair value hierarchy for its financial assets
Money market funds			$ 2,262	$ 3,012							$ 2,262	$ 3,012
Available-for-sale securities					4,025	6,429	18,605	16,719	14,470	22,970					4,025	6,429	18,605	16,719	14,470	22,970
Total assets			39,362	49,130							2,262	3,012	37,100	46,118
Transfer of assets between Level 1 to Level 2	0	0
Transfer of liabilities between Level 1 to Level 2	0	0
Transfer of assets between Level 2 to Level 1	0	0
Transfer of liabilities between Level 2 to Level 1	$ 0	$ 0