Business Segment and Geographic Region Information - Revenue by Product Line (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenue by product lines
Revenue	$ 105,683	$ 95,374	$ 119,333	$ 122,185	$ 116,396	$ 104,482	$ 102,790	$ 86,893	$ 442,575	$ 410,561	$ 266,980	$ 266,980
Ion implantation systems and services
Revenue by product lines
Revenue									421,747	391,051		248,885
Other systems and services
Revenue by product lines
Revenue									$ 20,828	$ 19,510		$ 18,095