Segment Information - Geographic region (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Segment Information
Total revenue	$ 18,730	$ 18,257	$ 15,008	$ 19,862	$ 29,499	$ 12,427	$ 26,150	$ 5,338	$ 71,857	$ 73,414	$ 60,370
United States
Segment Information
Total revenue									70,319	54,760	49,239
Europe
Segment Information
Total revenue									$ 1,538	$ 18,654	11,117
Asia
Segment Information
Total revenue											$ 14