Revenue - Schedule of Disaggregation of Revenue by Revenue Source (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Disaggregation Of Revenue [Line Items]
Total revenue	$ 73,096	$ 60,679
Systems Revenue [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	56,102	43,893
Software Revenue
Disaggregation Of Revenue [Line Items]
Total revenue	7,455	7,498
Parts Revenue
Disaggregation Of Revenue [Line Items]
Total revenue	6,985	6,330
Service Revenue
Disaggregation Of Revenue [Line Items]
Total revenue	$ 2,554	$ 2,958