Balance Sheet Accounts - Schedule of Other Noncurrent Assets, net (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Real estate held for entitlement and leasing	$ 101.7	$ 100.3
Deferred costs recoverable from the U.S. government	56.5	54.8
Receivable from Northrop Grumman Corporation for environmental remediation costs	42.0	46.5
Other	47.2	54.0
Other noncurrent assets, net	$ 247.4	$ 255.6

Amount of real estate investment property, net of accumulated depreciation, which may include the following: (1) land available-for-sale; (2) land available-for-development; (3) investments in building and building improvements; (4) tenant allowances; (5) developments in-process; (6) rental properties; and (7) other real estate investments.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.1(d))
-URI http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910

Name:	us-gaap_RealEstateInvestmentPropertyNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant