Commitments and Contingencies - Summary of Northrop Agreement Activity (Details) - Northrop [Member] $ in Millions	Dec. 31, 2016 USD ($)
Site Contingency [Line Items]
Total reimbursable costs under the Northrop Agreement	$ 189.7
Amount reimbursed through December 31, 2016	(119.2)
Potential future cost reimbursements available	70.5
Receivable from Northrop in excess of the annual limitation included in the consolidated balance sheet as of December 31, 2016	(68.0)
Potential future recoverable amounts available under the Northrop Agreement	$ 2.5