Segment and Geographic Information - Schedule of Product Revenue Based on Location (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Revenues From External Customers And Long Lived Assets [Line Items]
Product revenue	$ 7,269	$ 1,322
Type of Revenue [Extensible List]	us-gaap:ProductMember	us-gaap:ProductMember
United States
Revenues From External Customers And Long Lived Assets [Line Items]
Product revenue	$ 3,636	$ 897
Germany
Revenues From External Customers And Long Lived Assets [Line Items]
Product revenue	643	254
Rest of Europe
Revenues From External Customers And Long Lived Assets [Line Items]
Product revenue	2,736	129
All Other Countries
Revenues From External Customers And Long Lived Assets [Line Items]
Product revenue	$ 254	$ 42