Construction Joint Ventures - Schedule of Unconsolidated Construction Joint Ventures Assets and Liabilities (Parenthetical) (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017
Construction Joint Venture
Unconsolidated Joint Venture Back charges claims	$ 11.3	$ 11.8	$ 7.9
Deficit in unconsolidated construction joint venture	22.3	15.9	16.4
Unconsolidated Construction Joint Venture
Construction Joint Venture
Performance Guarantees	88.6	88.6	83.1
Unconsolidated Construction Joint Venture | Reporting Entitys Interest in Joint Venture [Member]
Construction Joint Venture
Affirmative Claim Recovery Estimate	$ 65.0	$ 74.3	$ 69.7