Revenue Recognition - Schedule of Percentage of Sales by Contract and Customer (Details) - Sales Revenue, Net	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Customers | U.S. government
Concentration Risk [Line Items]
Percentage of net sales	92.00%	93.00%
Customers | Non U.S. government customers
Concentration Risk [Line Items]
Percentage of net sales	8.00%	7.00%
Segment | Real Estate
Concentration Risk [Line Items]
Percentage of net sales	1.00%	1.00%
Fixed-price | Contract
Concentration Risk [Line Items]
Percentage of net sales	59.00%	56.00%
Cost-reimbursable | Contract
Concentration Risk [Line Items]
Percentage of net sales	38.00%	41.00%
Other | Contract
Concentration Risk [Line Items]
Percentage of net sales	3.00%	3.00%