Revenue - Schedule of Disaggregation of Revenue by Revenue Source (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Disaggregation Of Revenue [Line Items]
Total revenue	$ 60,892	$ 73,096
Systems Revenue [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	42,772	56,102
Software Revenue [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	7,037	7,455
Parts Revenue [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	8,077	6,985
Service Revenue [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	$ 3,006	$ 2,554