Segment Information - Geographic region (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Segment Information
Revenue	$ 29,499	$ 12,427	$ 26,150	$ 5,338	$ 15,737	$ 12,838	$ 23,476	$ 8,319	$ 73,414	$ 60,370	$ 15,386
United States
Segment Information
Revenue									54,760	49,239	14,272
Europe
Segment Information
Revenue									$ 18,654	11,117	1,109
Asia
Segment Information
Revenue										$ 14	$ 5