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, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Segment Reporting Information [Line Items]
Revenues	$ 61,511	$ 77,476	$ 122,403	$ 150,572
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	$ 44,253	$ 56,262	$ 83,411	$ 104,295
Process Control [Member] | Sales [Member] | Product [Member]
Segment Reporting Information [Line Items]
Concentration risk, percentage	72.00%	72.00%	68.00%	70.00%
Lithography [Member]
Segment Reporting Information [Line Items]
Revenues	$ 62	$ 3,851	$ 3,676	$ 11,921
Lithography [Member] | Sales [Member] | Product [Member]
Segment Reporting Information [Line Items]
Concentration risk, percentage		5.00%	3.00%	7.00%
Software Revenue [Member]
Segment Reporting Information [Line Items]
Revenues	$ 7,297	$ 7,547	$ 14,334	$ 15,002
Software Revenue [Member] | Sales [Member] | Product [Member]
Segment Reporting Information [Line Items]
Concentration risk, percentage	12.00%	10.00%	12.00%	10.00%
Parts Revenue [Member]
Segment Reporting Information [Line Items]
Revenues	$ 7,073	$ 6,758	$ 15,150	$ 13,742
Parts Revenue [Member] | Sales [Member] | Product [Member]
Segment Reporting Information [Line Items]
Concentration risk, percentage	11.00%	9.00%	12.00%	9.00%
Service Revenue [Member]
Segment Reporting Information [Line Items]
Revenues	$ 2,826	$ 3,058	$ 5,832	$ 5,612
Service Revenue [Member] | Sales [Member] | Product [Member]
Segment Reporting Information [Line Items]
Concentration risk, percentage	5.00%	4.00%	5.00%	4.00%