Revenue - Disaggregated by category (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Disaggregation of Revenue [Line Items]
Total revenues	$ 66,548	$ 168,493	$ 220,687	$ 327,368
Revenue as a percentage	100.00%	100.00%	100.00%	100.00%
Product revenue
Disaggregation of Revenue [Line Items]
Total revenues	$ 40,893	$ 94,494	$ 127,924	$ 181,134
Revenue as a percentage	62.00%	56.00%	58.00%	55.00%
Rental revenue
Disaggregation of Revenue [Line Items]
Total revenues	$ 11,535	$ 39,576	$ 47,698	$ 78,073
Revenue as a percentage	17.00%	24.00%	22.00%	24.00%
Field service and other revenue
Disaggregation of Revenue [Line Items]
Total revenues	$ 14,120	$ 34,423	$ 45,065	$ 68,161
Revenue as a percentage	21.00%	20.00%	20.00%	21.00%