Segment Reporting and Geographic Information (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($) item segment	Sep. 30, 2017 USD ($)
Revenue reporting by end-market and geographic region
Number of operating segments | segment			1
Number of reportable segments | segment			1
Number of key markets | item			4
Sale by end-market	$ 126,757	$ 129,308	$ 443,110	$ 336,025
United States
Revenue reporting by end-market and geographic region
Sale by end-market	28,861	34,914	85,555	72,820
China
Revenue reporting by end-market and geographic region
Sale by end-market	39,200	12,956	185,050	81,121
EMEA
Revenue reporting by end-market and geographic region
Sale by end-market	30,685	16,948	71,836	54,140
Rest Of World
Revenue reporting by end-market and geographic region
Sale by end-market	28,011	64,490	100,669	127,944
Advanced Packaging, MEMS & RF Filters
Revenue reporting by end-market and geographic region
Sale by end-market	24,562	21,478	76,473	54,216
LED Lighting, Display & Compound Semiconductor
Revenue reporting by end-market and geographic region
Sale by end-market	58,864	57,647	236,597	167,105
Front-End Semiconductor
Revenue reporting by end-market and geographic region
Sale by end-market	13,476	16,256	41,085	27,736
Scientific & Industrial
Revenue reporting by end-market and geographic region
Sale by end-market	$ 29,855	$ 33,927	$ 88,955	$ 86,968