Revenue Recognition - Schedule of Percentage of Sales by Contract and Customer (Details) - Sales Revenue, Net	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Customers | U.S. government
Concentration Risk [Line Items]
Percentage of net sales	93.00%	93.00%	93.00%	93.00%
Customers | Non U.S. government customers
Concentration Risk [Line Items]
Percentage of net sales	7.00%	7.00%	7.00%	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	58.00%	58.00%	59.00%	57.00%
Cost-reimbursable | Contract
Concentration Risk [Line Items]
Percentage of net sales	39.00%	37.00%	38.00%	39.00%
Other | Contract
Concentration Risk [Line Items]
Percentage of net sales	3.00%	5.00%	3.00%	4.00%