Segment Reporting and Geographic Information - Schedule of Revenue from External Customers by Products and Services (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Segment Reporting Information [Line Items]
Revenues	$ 60,432	$ 66,920	$ 211,004	$ 195,017
Sales [Member] | Product [Member]
Segment Reporting Information [Line Items]
Concentration risk, percentage	100.00%	100.00%	100.00%	100.00%
Process Control [Member]
Segment Reporting Information [Line Items]
Revenues	$ 41,164	$ 43,821	$ 145,458	$ 135,408
Process Control [Member] | Sales [Member] | Product [Member]
Segment Reporting Information [Line Items]
Concentration risk, percentage	68.00%	65.00%	69.00%	70.00%
Lithography [Member]
Segment Reporting Information [Line Items]
Revenues	$ 2,791	$ 7,010	$ 14,712	$ 10,560
Lithography [Member] | Sales [Member] | Product [Member]
Segment Reporting Information [Line Items]
Concentration risk, percentage	5.00%	11.00%	7.00%	5.00%
Software Revenue [Member]
Segment Reporting Information [Line Items]
Revenues	$ 6,877	$ 6,053	$ 21,879	$ 20,447
Software Revenue [Member] | Sales [Member] | Product [Member]
Segment Reporting Information [Line Items]
Concentration risk, percentage	11.00%	9.00%	10.00%	10.00%
Parts [Member]
Segment Reporting Information [Line Items]
Revenues	$ 7,141	$ 7,101	$ 20,884	$ 20,779
Parts [Member] | Sales [Member] | Product [Member]
Segment Reporting Information [Line Items]
Concentration risk, percentage	12.00%	11.00%	10.00%	11.00%
Services [Member]
Segment Reporting Information [Line Items]
Revenues	$ 2,459	$ 2,935	$ 8,071	$ 7,823
Services [Member] | Sales [Member] | Product [Member]
Segment Reporting Information [Line Items]
Concentration risk, percentage	4.00%	4.00%	4.00%	4.00%