Fair Value of Financial Instruments (Details) (Recurring basis, USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Level 1
Fair Value of Financial Instruments
Total fair value of financial assets	$ 106,999	$ 121,466
Level 1 | Money market funds
Fair Value of Financial Instruments
Total fair value of financial assets	106,999	121,466
Level 2
Fair Value of Financial Instruments
Total fair value of financial assets	25	3,219
Level 2 | Certificates of deposit
Fair Value of Financial Instruments
Total fair value of financial assets	$ 25	$ 3,219