Geographic Information (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Geographic Information
Total revenue	$ 10,123	$ 9,008	$ 8,925	$ 7,880	$ 7,064	$ 7,164	$ 6,659	$ 6,207	$ 35,936	$ 27,094	$ 26,546
United States
Geographic Information
Total revenue									4,759	4,321	5,362
Singapore
Geographic Information
Total revenue									8,067	5,467	4,614
Japan
Geographic Information
Total revenue									4,128	3,285	2,280
Germany
Geographic Information
Total revenue									2,964	3,013	3,546
Taiwan
Geographic Information
Total revenue									2,076	2,161	3,759
Hong Kong
Geographic Information
Total revenue									2,179	2,122	2,744
All other
Geographic Information
Total revenue									$ 11,763	$ 6,725	$ 4,241