Revenues - Product revenue by type (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Revenue from External Customer [Line Items]
Total revenues	$ 217,413	$ 188,673	$ 419,930	$ 371,292
Hardware and software
Revenue from External Customer [Line Items]
Total revenues	135,022	112,031	255,243	219,482
Consumables
Revenue from External Customer [Line Items]
Total revenues	19,416	19,670	40,503	39,108
Other
Revenue from External Customer [Line Items]
Total revenues	3,941	2,935	8,243	6,705
Product revenues
Revenue from External Customer [Line Items]
Total revenues	$ 158,379	$ 134,636	$ 303,989	$ 265,295