Commitments and Contingencies - Narrative - Environmental Reserves and Estimated Recoveries (Details) - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2017	Nov. 30, 2003	Mar. 31, 2020
Site Contingency [Line Items]
Non-reimbursable percentage of environmental costs			12.00%
Northrop
Site Contingency [Line Items]
Percentage of environmental remediation costs recoverable			88.00%
Current annual billing limitation			$ 6,000,000.0
Reimbursable remediation cost			$ 189,700,000
Atlantic Research Corporation
Site Contingency [Line Items]
Pre-close environmental costs	$ 20,000,000.0	$ 20,000,000.0