Fair Value Measurements - Additional Information (Details) - USD ($)	Sep. 30, 2017	Dec. 31, 2016
Fair Value, Measurement Inputs, Disclosure [Line Items]
Liabilities, Fair Value Disclosure, Recurring	$ 0
Long-term investments
Fair Value, Assets, Level 1 to Level 2 Transfers, Amount	0
Fair Value, Inputs, Level 1
Cash and cash equivalents
Cash	44,296,000	$ 49,495,000
Money market funds	56,500,000	56,208,000
Total cash and cash equivalents	100,796,000	105,703,000
Short-term investments	51,000	63,000
Long-term investments
Restricted cash, at fair value	1,181,000	1,181,000
Total cash and cash equivalents and investments	$ 102,028,000	$ 106,947,000