Revenue - Schedule of Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Disaggregation of Revenue [Line Items]
Total revenue	$ 133,145	$ 120,936	$ 297,776	$ 284,194
Unapproved change orders	1,655		1,655
Environmental Solutions
Disaggregation of Revenue [Line Items]
Total revenue	37,862	36,950	74,527	95,333
Environmental Solutions | United States
Disaggregation of Revenue [Line Items]
Total revenue	37,651	36,950	73,681	95,333
Environmental Solutions | Foreign
Disaggregation of Revenue [Line Items]
Total revenue	211	0	846	0
Maintenance and Technical Services
Disaggregation of Revenue [Line Items]
Total revenue	95,283	83,986	223,249	188,861
Maintenance and Technical Services | United States
Disaggregation of Revenue [Line Items]
Total revenue	95,283	83,986	223,249	188,861
Product sales | Environmental Solutions
Disaggregation of Revenue [Line Items]
Total revenue	21,400	24,890	43,161	47,402
Construction contracts | Environmental Solutions
Disaggregation of Revenue [Line Items]
Total revenue	15,347	11,900	30,194	46,207
Services | Environmental Solutions
Disaggregation of Revenue [Line Items]
Total revenue	1,115	160	1,172	1,724
Services | Maintenance and Technical Services
Disaggregation of Revenue [Line Items]
Total revenue	$ 95,283	$ 83,986	$ 223,249	$ 188,861