Accrued Expenses - Schedule of Accrued Expenses (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Accrued Liabilities And Other Liabilities [Abstract]
Employee compensation and benefits	$ 14,170	$ 19,707
Project related reimbursable expenses	45,145	0
Other	4,261	3,966
Total accrued expenses	$ 63,576	$ 23,673