Segment Reporting and Geographic Information - Schedule of Revenue from External Customers by Products and Services (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting Information [Line Items]
Revenues	$ 273,784	$ 255,098	$ 232,780
Sales [Member] | Product [Member]
Segment Reporting Information [Line Items]
Concentration risk, percentage	100.00%	100.00%	100.00%
Process Control [Member]
Segment Reporting Information [Line Items]
Revenues	$ 190,098	$ 177,177	$ 146,652
Process Control [Member] | Sales [Member] | Product [Member]
Segment Reporting Information [Line Items]
Concentration risk, percentage	70.00%	70.00%	63.00%
Lithography [Member]
Segment Reporting Information [Line Items]
Revenues	$ 14,975	$ 14,234	$ 18,949
Lithography [Member] | Sales [Member] | Product [Member]
Segment Reporting Information [Line Items]
Concentration risk, percentage	5.00%	5.00%	8.00%
Software Revenue [Member]
Segment Reporting Information [Line Items]
Revenues	$ 29,168	$ 25,473	$ 29,795
Software Revenue [Member] | Sales [Member] | Product [Member]
Segment Reporting Information [Line Items]
Concentration risk, percentage	11.00%	10.00%	13.00%
Parts Revenue [Member]
Segment Reporting Information [Line Items]
Revenues	$ 28,658	$ 27,143	$ 25,343
Parts Revenue [Member] | Sales [Member] | Product [Member]
Segment Reporting Information [Line Items]
Concentration risk, percentage	10.00%	11.00%	11.00%
Service Revenue [Member]
Segment Reporting Information [Line Items]
Revenues	$ 10,885	$ 11,071	$ 12,041
Service Revenue [Member] | Sales [Member] | Product [Member]
Segment Reporting Information [Line Items]
Concentration risk, percentage	4.00%	4.00%	5.00%