Accounts Payable and Accrued Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Accounts Payable and Accrued Liabilities
Retention amounts included in accounts payable	$ 13,500	$ 10,600
Accrued expenses and other current liabilities
Payroll and related employee benefits	45,708	43,768
Insurance, including self-insurance reserves	47,256	42,546
Reserve for estimated losses on uncompleted contracts	10,067	12,801
Corporate income taxes and other taxes	2,843	3,368
Other	5,513	5,523
Total accrued expenses and other current liabilities	$ 111,387	$ 108,006