Revenue (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Revenue [Abstract]
Revenue performance obligation	The Company’s contracts typically provide for termination by either party within 30 to 90 days. Although payment terms vary by client, they are typically within 30 to 60 days.
Customer Advances, Current	$ 138,505	$ 148,133
Unbilled Contracts Receivable	64,362	54,177
Expenditures Billable Current	$ 42,369	$ 31,146