Accounts Receivable (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Trade accounts receivable	$ 174,604	$ 119,239
Costs in excess of billings	26,915	20,607
Total contract receivables	201,519	139,846
Less allowance for doubtful accounts	(3,529)	(5,951)	$ (6,170)	$ (5,599)
Accounts receivable	197,990	$ 133,895
Thermo Energy Systems Inc., Delta Separations, LLC, Architectural Mailboxes LLC , Sunfig Corporation, and TerraSmart LLC
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable	$ 62,000