Revenue - Schedule of Disaggregation of Revenue by Revenue Source (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Disaggregation Of Revenue [Line Items]
Total revenue	$ 61,511	$ 77,476	$ 122,403	$ 150,572
Systems Revenue [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	44,315	60,113	87,087	116,216
Software Revenue [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	7,297	7,547	14,334	15,002
Parts Revenue [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	7,073	6,758	15,150	13,742
Service Revenue [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	$ 2,826	$ 3,058	$ 5,832	$ 5,612