Segment Reporting and Significant Customers (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($) segment	Jun. 30, 2017 USD ($)
Segment Reporting and Significant Customers
Number of reporting segment | segment			1
Total revenue	$ 10,938	$ 6,042	$ 20,980	$ 11,339
United States
Segment Reporting and Significant Customers
Total revenue	9,529	4,867	18,272	9,375
Europe
Segment Reporting and Significant Customers
Total revenue	$ 1,409	$ 1,175	$ 2,708	$ 1,964