Construction Joint Ventures - Schedule of Unconsolidated Construction Joint Ventures Assets and Liabilities (Parenthetical) (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017
Construction Joint Venture
Performance Guarantees	$ 88.6	$ 88.6	$ 88.9
Unconsolidated Joint Venture Back charges claims	10.6	11.8	9.8
Deficit in unconsolidated construction joint venture	14.7	15.9	15.9
Reporting Entitys Interest in Joint Venture [Member]
Construction Joint Venture
Affirmative Claim Recovery Estimate	$ 65.8	$ 74.3	$ 81.7