Revenue (Details)	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Product revenue
Disaggregation of revenues
Total revenue	56.00%	52.00%
Rental revenue
Disaggregation of revenues
Total revenue	23.00%	25.00%
Field service and other revenue
Disaggregation of revenues
Total revenue	21.00%	23.00%