Segment Reporting - Geographic Information (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Geographical Information
Revenues, total	$ 37,256	$ 86,390	$ 81,013	$ 271,385
Greater China [Member]
Geographical Information
Revenues, total	19,346	26,557	26,008	85,813
Western Europe [Member]
Geographical Information
Revenues, total	5,085	8,433	10,273	28,809
Asia (excluding China) [Member]
Geographical Information
Revenues, total	4,935	13,534	12,663	32,287
United States [Member]
Geographical Information
Revenues, total	4,335	24,316	21,112	84,553
Latin America [Member]
Geographical Information
Revenues, total	1,616	2,912	3,251	7,725
Russia & the CIS [Member]
Geographical Information
Revenues, total	738	2,909	2,962	10,216
Canada [Member]
Geographical Information
Revenues, total	384	1,993	1,327	6,485
Rest of the World [Member]
Geographical Information
Revenues, total	$ 817	$ 5,736	$ 3,417	$ 15,497