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Derivative Instruments - Narrative (Details) - USD ($)
$ in Millions
3 Months Ended 9 Months Ended
Sep. 30, 2017
Sep. 30, 2016
Sep. 30, 2017
Sep. 30, 2016
Dec. 31, 2016
Nov. 01, 2016
Nov. 01, 2015
Derivative [Line Items]              
Gain on derivative $ 1.0            
Unrealized losses on derivatives     $ 12.0        
Derivative asset 3.3 $ 4.1 3.3 $ 4.1 $ 18.8    
Derivative liability 12.6 5.1 12.6 5.1 0.7    
Derivative, fair value $ 9.3 1.0 $ 9.3 1.0 $ 18.1    
Derivative, Loss on Derivative   $ 1.0   $ 24.1      
2016 - 2017              
Derivative [Line Items]              
Target hedge percentage, 2016 - 2017           75.00%  
2015 - 2016              
Derivative [Line Items]              
Target hedge percentage, 2016 - 2017             75.00%