Segment Reporting and Geographic Information - Schedule of Revenue from External Customers by Products and Services (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Segment Reporting Information [Line Items]
Revenues	$ 77,476	$ 67,418	$ 150,572	$ 128,097
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	$ 56,262	$ 47,711	$ 104,295	$ 91,586
Process Control [Member] | Sales [Member] | Product [Member]
Segment Reporting Information [Line Items]
Concentration risk, percentage	72.00%	71.00%	70.00%	72.00%
Lithography [Member]
Segment Reporting Information [Line Items]
Revenues	$ 3,851	$ 3,533	$ 11,921	$ 3,550
Lithography [Member] | Sales [Member] | Product [Member]
Segment Reporting Information [Line Items]
Concentration risk, percentage	5.00%	5.00%	7.00%	2.00%
Software Revenue [Member]
Segment Reporting Information [Line Items]
Revenues	$ 7,547	$ 6,895	$ 15,002	$ 14,394
Software Revenue [Member] | Sales [Member] | Product [Member]
Segment Reporting Information [Line Items]
Concentration risk, percentage	10.00%	10.00%	10.00%	11.00%
Parts [Member]
Segment Reporting Information [Line Items]
Revenues	$ 6,758	$ 7,348	$ 13,742	$ 13,678
Parts [Member] | Sales [Member] | Product [Member]
Segment Reporting Information [Line Items]
Concentration risk, percentage	9.00%	11.00%	9.00%	11.00%
Services [Member]
Segment Reporting Information [Line Items]
Revenues	$ 3,058	$ 1,931	$ 5,612	$ 4,889
Services [Member] | Sales [Member] | Product [Member]
Segment Reporting Information [Line Items]
Concentration risk, percentage	4.00%	3.00%	4.00%	4.00%