Revenue - Disaggregated by category (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Disaggregation of Revenue [Line Items]
Total revenues	$ 59,789	$ 160,808	$ 280,476	$ 488,176
Revenue as a percentage	100.00%	100.00%	100.00%	100.00%
Product revenue
Disaggregation of Revenue [Line Items]
Total revenues	$ 35,857	$ 92,582	$ 163,781	$ 273,716
Revenue as a percentage	60.00%	58.00%	58.00%	56.00%
Rental revenue
Disaggregation of Revenue [Line Items]
Total revenues	$ 9,881	$ 35,528	$ 57,579	$ 113,601
Revenue as a percentage	17.00%	22.00%	21.00%	23.00%
Field service and other revenue
Disaggregation of Revenue [Line Items]
Total revenues	$ 14,051	$ 32,698	$ 59,116	$ 100,859
Revenue as a percentage	23.00%	20.00%	21.00%	21.00%