Segment Reporting - Additional Information (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($) Segment	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Segment Reporting Information [Line Items]
Number of reportable segments | Segment	1
Description of long-lived assets located	Substantially all our long-lived assets are located in the United States.
Total revenue	$ 122,633	$ 125,300	$ 112,287
United States
Segment Reporting Information [Line Items]
Total revenue	29,500	28,800	25,900
China
Segment Reporting Information [Line Items]
Total revenue	$ 64,300	$ 68,000	$ 59,300