Revenue (Details) - Systems	3 Months Ended
	Mar. 31, 2019
Disaggregation of Revenue
Payment upon shipment of tool, as a percent	90.00%
Payment upon installation, as a percent	10.00%
Minimum
Disaggregation of Revenue
Payment upon delivery of parts, period	30 days
Maximum
Disaggregation of Revenue
Payment upon delivery of parts, period	60 days