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, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Segment Reporting Information [Line Items]
Revenues	$ 66,920	$ 61,641	$ 195,017	$ 178,704
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	$ 43,821	$ 41,485	$ 135,408	$ 112,407
Process Control [Member] | Sales [Member] | Product [Member]
Segment Reporting Information [Line Items]
Concentration risk, percentage	65.00%	67.00%	70.00%	63.00%
Lithography [Member]
Segment Reporting Information [Line Items]
Revenues	$ 7,010	$ 3,846	$ 10,560	$ 15,496
Lithography [Member] | Sales [Member] | Product [Member]
Segment Reporting Information [Line Items]
Concentration risk, percentage	11.00%	6.00%	5.00%	8.00%
Software [Member]
Segment Reporting Information [Line Items]
Revenues	$ 6,053	$ 7,379	$ 20,447	$ 22,581
Software [Member] | Sales [Member] | Product [Member]
Segment Reporting Information [Line Items]
Concentration risk, percentage	9.00%	12.00%	10.00%	13.00%
Parts [Member]
Segment Reporting Information [Line Items]
Revenues	$ 7,101	$ 5,973	$ 20,779	$ 19,126
Parts [Member] | Sales [Member] | Product [Member]
Segment Reporting Information [Line Items]
Concentration risk, percentage	11.00%	10.00%	11.00%	11.00%
Services [Member]
Segment Reporting Information [Line Items]
Revenues	$ 2,935	$ 2,958	$ 7,823	$ 9,094
Services [Member] | Sales [Member] | Product [Member]
Segment Reporting Information [Line Items]
Concentration risk, percentage	4.00%	5.00%	4.00%	5.00%