Revenue - Revenue by discipline & geographical areas (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Disaggregation of Revenue
Total Revenue	$ 147,274	$ 122,965	$ 280,050	$ 241,956
North America
Disaggregation of Revenue
Total Revenue	10,204	8,915	19,712	19,576
Asia Pacific
Disaggregation of Revenue
Total Revenue	116,642	106,604	220,033	203,432
Europe
Disaggregation of Revenue
Total Revenue	20,428	7,446	40,305	18,948
Systems
Disaggregation of Revenue
Total Revenue	100,138	76,815	181,129	159,152
CS&I/Aftermarket
Disaggregation of Revenue
Total Revenue	$ 47,136	$ 46,150	$ 98,921	$ 82,804