Revenues - Product revenue by type (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Revenue from External Customer [Line Items]
Total revenues	$ 228,805	$ 204,267	$ 648,735	$ 575,559
Hardware and software
Revenue from External Customer [Line Items]
Total revenues	144,305	125,733	399,548	345,215
Consumables
Revenue from External Customer [Line Items]
Total revenues	19,875	19,848	60,378	58,956
Other
Revenue from External Customer [Line Items]
Total revenues	4,308	4,128	12,551	10,833
Product revenues
Revenue from External Customer [Line Items]
Total revenues	$ 168,488	$ 149,709	$ 472,477	$ 415,004