Segment Reporting and Geographic Information Segment Reporting (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Segment Reporting Information [Line Items]
Revenues	$ 54,076	$ 61,641	$ 62,701	$ 54,362	$ 51,057	$ 58,597	$ 59,466	$ 52,570	$ 232,780	$ 221,690	$ 181,218
Process Control Revenue [Member]
Segment Reporting Information [Line Items]
Revenues									146,652	144,858	112,408
Lithography Revenue [Domain]
Segment Reporting Information [Line Items]
Revenues									18,949	14,519	11,163
Software [Domain]
Segment Reporting Information [Line Items]
Revenues									29,795	27,291	24,042
Sales Revenue, Goods, Net [Member]
Segment Reporting Information [Line Items]
Revenues									25,343	24,072	20,334
Sales Revenue, Services, Net [Member]
Segment Reporting Information [Line Items]
Revenues									12,041	10,950	13,271
Sales Revenue, Segment [Member]
Segment Reporting Information [Line Items]
Revenues									$ 232,780	$ 221,690	$ 181,218
Sales [Member] | Percentage of Process Control Revenue [Member]
Segment Reporting Information [Line Items]
Concentration Risk, Percentage									63.00%	66.00%	63.00%
Sales [Member] | Percentage of Lithography Revenue [Member] [Domain]
Segment Reporting Information [Line Items]
Concentration Risk, Percentage									8.00%	6.00%	6.00%
Sales [Member] | Percentage of Software Revenue [Domain]
Segment Reporting Information [Line Items]
Concentration Risk, Percentage									13.00%	12.00%	13.00%
Sales [Member] | Percentage of Parts [Member]
Segment Reporting Information [Line Items]
Concentration Risk, Percentage									11.00%	11.00%	11.00%
Sales [Member] | Percentage of Service [Member]
Segment Reporting Information [Line Items]
Concentration Risk, Percentage									5.00%	5.00%	7.00%
Sales [Member] | Percentage of Total Revenue [Member]
Segment Reporting Information [Line Items]
Concentration Risk, Percentage									100.00%	100.00%	100.00%