Commitments and Contingencies - Summary of Northrop Agreement Activity (Details) - Northrop - USD ($) $ in Millions	Sep. 30, 2017	Jun. 30, 2017
Contingencies And Commitments [Line Items]
Total reimbursable costs under the Northrop Agreement	$ 189.7
Amount reimbursed to the Company through September 30, 2017	(123.7)
Potential future cost reimbursements available	66.0
Less: Receivable from Northrop included in the unaudited condensed consolidated balance sheet as of September 30, 2017	(66.0)
Potential future recoverable amounts available under the Northrop Agreement	$ 0.0
Maximum
Contingencies And Commitments [Line Items]
Total reimbursable costs under the Northrop Agreement		$ 189.7