v3.4.0.3
Segment and geographic information - Risk (Details) - Revenues, net - Consolidated revenue
3 Months Ended
Mar. 31, 2016
Mar. 31, 2015
Independent Electricity System Operator    
Consolidated revenue concentration    
Percentage of consolidated revenue 38.10% 33.70%
San Diego Gas & Electric    
Consolidated revenue concentration    
Percentage of consolidated revenue   14.40%
BC Hydro    
Consolidated revenue concentration    
Percentage of consolidated revenue 14.20% 11.70%
Niagara Mohawk    
Consolidated revenue concentration    
Percentage of consolidated revenue 9.90%