Revenue - Revenue by discipline & geographical areas (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Disaggregation of Revenue
Total Revenue	$ 176,694	$ 110,405	$ 456,744	$ 352,361
North America
Disaggregation of Revenue
Total Revenue	11,847	9,022	31,560	28,598
Asia Pacific
Disaggregation of Revenue
Total Revenue	137,870	89,995	357,903	293,427
Europe
Disaggregation of Revenue
Total Revenue	26,977	11,388	67,281	30,336
Systems
Disaggregation of Revenue
Total Revenue	126,166	70,239	307,295	229,391
CS&I/Aftermarket
Disaggregation of Revenue
Total Revenue	$ 50,528	$ 40,166	$ 149,449	$ 122,970