Fair Value Measurements - Additional Information (Details) - USD ($)	Jun. 30, 2016	Dec. 31, 2015	Jun. 30, 2015	Dec. 31, 2014
Cash and cash equivalents
Cash	$ 41,905,000	$ 33,764,000
Money market funds	54,756,000	54,745,000
Total cash and cash equivalents	96,661,000	88,509,000	$ 85,598,000	$ 89,955,000
Long-term investments
Total cash and cash equivalents and investments	99,259,000	91,107,000
Restricted cash, at fair value	2,598,000	$ 2,598,000
Fair Value, Assets, Level 1 to Level 2 Transfers, Amount	0
Fair Value, Inputs, Level 1
Long-term investments
Cash and cash equivalents, at fair value	96,700,000
Restricted cash, at fair value	$ 2,600,000