Construction Joint Ventures - Schedule of Unconsolidated Construction Joint Ventures Assets and Liabilities (Parenthetical) (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017
Construction Joint Venture
Performance Guarantees	$ 88.6	$ 88.6	$ 88.9
Unconsolidated Joint Venture Back charges claims	12.5	11.8	11.1
Deficit in unconsolidated construction joint venture	11.6	15.9	16.0
Reporting Entitys Interest in Joint Venture [Member]
Construction Joint Venture
Affirmative Claim Recovery Estimate	$ 67.1	$ 74.3	$ 77.6