Revenue - Schedule of Disaggregation of Revenue by Revenue Source (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Disaggregation Of Revenue [Line Items]
Total revenue	$ 77,476	$ 67,418	$ 150,572	$ 128,097
Systems Revenue [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	60,113	51,244	116,216	95,136
Software Revenue [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	7,547	6,895	15,002	14,394
Parts Revenue [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	6,758	7,348	13,742	13,678
Service Revenue [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	$ 3,058	$ 1,931	$ 5,612	$ 4,889