Segment Reporting and Geographic Information (Details) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Segment Reporting Information [Line Items]
Revenues	$ 51,057,000	$ 58,597,000	$ 59,466,000	$ 52,570,000	$ 49,591,000	$ 46,960,000	$ 43,018,000	$ 41,649,000	$ 221,690,000	$ 181,218,000	$ 176,238,000
UNITED STATES
Segment Reporting Information [Line Items]
Revenues									46,778,000	56,963,000	40,849,000
Taiwan [Member]
Segment Reporting Information [Line Items]
Revenues									55,548,000	49,532,000	54,682,000
South Korea [Member]
Segment Reporting Information [Line Items]
Revenues									14,221,000	16,690,000	10,704,000
Singapore [Member]
Segment Reporting Information [Line Items]
Revenues									27,310,000	14,551,000	15,804,000
Austria [Domain]
Segment Reporting Information [Line Items]
Revenues									3,557,000	752,000	898,000
JAPAN
Segment Reporting Information [Line Items]
Revenues									13,216,000	9,449,000	7,326,000
GERMANY
Segment Reporting Information [Line Items]
Revenues									29,378,000	9,142,000	5,669,000
CHINA
Segment Reporting Information [Line Items]
Revenues									17,152,000	11,521,000	20,061,000
Sales [Member]
Segment Reporting Information [Line Items]
Revenues									221,690,000	181,218,000	176,238,000
Other Europe [Member]
Segment Reporting Information [Line Items]
Revenues									11,403,000	9,362,000	18,789,000
Asia [Member]
Segment Reporting Information [Line Items]
Revenues									3,127,000	3,256,000	1,456,000
Inspection Revenue [Member]
Segment Reporting Information [Line Items]
Revenues									118,925,000	87,818,000	89,089,000
Percentage of Inspection Revenues [Member]
Segment Reporting Information [Line Items]
Revenues									0.54	0.49	0.51
Metrology Revenue [Member]
Segment Reporting Information [Line Items]
Revenues									25,933,000	24,590,000	26,500,000
Percentage of Metrology Revenue [Member]
Segment Reporting Information [Line Items]
Revenues									0.12	0.14	0.15
Data Analysis & Review [Member]
Segment Reporting Information [Line Items]
Revenues									27,291,000	24,042,000	17,927,000
Percentage of Data Analysis & Review [Member]
Segment Reporting Information [Line Items]
Revenues									0.12	0.13	0.10
Lithography [Domain]
Segment Reporting Information [Line Items]
Revenues									14,519,000	11,163,000	8,548,000
Percentage of Lithography [Domain]
Segment Reporting Information [Line Items]
Revenues									0.06	0.06	0.05
Sales Revenue, Goods, Net [Member]
Segment Reporting Information [Line Items]
Revenues									24,072,000	20,334,000	21,078,000
Percentage of Parts [Member]
Segment Reporting Information [Line Items]
Revenues									0.11	0.11	0.12
Sales Revenue, Services, Net [Member]
Segment Reporting Information [Line Items]
Revenues									10,950,000	13,271,000	13,096,000
Percentage of Service [Member]
Segment Reporting Information [Line Items]
Revenues									0.05	0.07	0.07
Sales [Member]
Segment Reporting Information [Line Items]
Revenues									221,690,000	181,218,000	176,238,000
Percentage of Total Revenue [Member]
Segment Reporting Information [Line Items]
Revenues									$ 1.00	$ 1.00	$ 1.00
Major Customer, One [Domain]
Segment Reporting Information [Line Items]
Concentration Risk, Percentage											11.40%
Major Customers Two [Domain]
Segment Reporting Information [Line Items]
Concentration Risk, Percentage											10.30%