Commitments and Contingencies - Summary of Northrop Agreement Activity (Details) - Northrop $ in Millions	Mar. 31, 2018 USD ($)
Contingencies And Commitments [Line Items]
Total reimbursable costs under the Northrop Agreement	$ 189.7
Amount reimbursed to the Company through March 31, 2018	(126.7)
Potential future cost reimbursements available	$ 63.0