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Subsequent Events (Detail) - USD ($)
$ in Millions
1 Months Ended 3 Months Ended 12 Months Ended
Apr. 30, 2016
Mar. 31, 2016
Mar. 31, 2015
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Subsequent Event [Line Items]            
Proceeds from sale of assets   $ 0.8 $ 0.5 $ 2.7 $ 2.7 $ 11.2
Subsequent Event            
Subsequent Event [Line Items]            
Proceeds from sale of assets $ 975.0          
CEGP | Subsequent Event            
Subsequent Event [Line Items]            
Ownership Percentage 50.00%