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Business Combinations - Other Acquisitions Narrative (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2016
Sep. 30, 2017
Nov. 01, 2016
CWind Limited      
Business Acquisition [Line Items]      
Percentage of ownership interest acquired 60.00%   40.00%
Series of Individually Immaterial Business Acquisitions      
Business Acquisition [Line Items]      
Consideration paid $ 14.9    
Cash paid in acquisition $ 9.2    
Scenario, Forecast | CWind Limited      
Business Acquisition [Line Items]      
Percentage of ownership interest acquired   40.00%