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Cash and Cash Equivalents (Details) - USD ($)
$ in Millions
Mar. 31, 2018
Dec. 31, 2017
Other assets    
Cash and Cash Equivalents [Line Items]    
Restricted cash and cash equivalents $ 3.0 $ 3.0
Other current assets    
Cash and Cash Equivalents [Line Items]    
Restricted cash and cash equivalents 0.6 0.6
Less than wholly-owned subsidiaries    
Cash and Cash Equivalents [Line Items]    
Restricted cash and cash equivalents 16.0 31.1
Majority-owned Joint Ventures    
Cash and Cash Equivalents [Line Items]    
Restricted cash and cash equivalents $ 9.8 $ 18.9