Accounts Payable and Accrued Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Accounts Payable and Accrued Liabilities
Accounts payable	$ 241,288	$ 140,943
Retention amounts included in accounts payable	14,700	13,500
Accrued expenses and other current liabilities
Payroll and related employee benefits	71,661	45,708
Insurance, including self-insurance reserves	31,400	21,391
Corporate income taxes and other taxes	8,151	2,843
Other	19,170	6,085
Total accrued expenses and other current liabilities	$ 130,382	$ 76,027