Revenue (Details)	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Product revenue
Disaggregation of revenues
Percentage of revenues	55.00%	52.00%
Rental revenue
Disaggregation of revenues
Percentage of revenues	24.00%	25.00%
Field service and other revenue
Disaggregation of revenues
Percentage of revenues	21.00%	23.00%
United States
Disaggregation of revenues
Percentage of revenues	99.00%