Revenue (Tables)

6 Months Ended

Jun. 30, 2019

Revenue From Contract With Customer [Abstract]

Schedule of Disaggregation of Revenue

The following table presents the Company’s revenue disaggregated by revenue source:

	Three Months Ended				Six Months Ended
	June 30,				June 30,
	2019		2018		2019		2018
Systems	$	44,315	$	60,113	$	87,087	$	116,216
Software licensing, support and     maintenance		7,297		7,547		14,334		15,002
Parts		7,073		6,758		15,150		13,742
Services		2,826		3,058		5,832		5,612
Total revenue	$	61,511	$	77,476	$	122,403	$	150,572

The following table represents a disaggregation of revenue by timing of revenue:

	Three Months Ended				Six Months Ended
	June 30,				June 30,
	2019		2018		2019		2018
Point-in-time	$	57,308	$	73,283	$	113,899	$	142,679
Over-time		4,203		4,193		8,504		7,893
Total revenue	$	61,511	$	77,476	$	122,403	$	150,572

Schedule of Changes in Deferred Revenue

Changes in deferred revenue were as follows:

	Three Months Ended						Six Months Ended
	June 30,						June 30,
	2019			2018			2019			2018
Balance, beginning of the period	$	8,687		$	8,773		$	8,080		$	7,206
Deferral of revenue		6,130			1,601			11,631			6,154
Recognition of deferred revenue		(5,468	)		(1,575	)		(10,362	)		(4,561	)
Balance, ending of the period	$	9,349		$	8,799		$	9,349		$	8,799