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Commitments and Contingencies - Rental Costs (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Commitments and Contingencies [Line Items]      
Rent expense $ 28.6 $ 22.2 $ 23.6
Unconsolidated real estate affiliates      
Commitments and Contingencies [Line Items]      
Rent expense $ 6.0 $ 5.9 $ 6.8