v3.4.0.3
Accounting for derivative instruments and hedging activities (Details)
CAD in Millions, $ in Millions
1 Months Ended 3 Months Ended 12 Months Ended
May. 05, 2014
USD ($)
May. 05, 2014
USD ($)
Jun. 30, 2014
MMBTU
Mar. 31, 2016
USD ($)
MMBTU
Mar. 31, 2015
USD ($)
Dec. 31, 2015
USD ($)
MMBTU
Mar. 31, 2016
CAD
item
Mar. 31, 2016
USD ($)
item
Feb. 14, 2014
USD ($)
Derivative instruments                  
Derivative Number of Contracts Designated as Cash Flow Hedges | item             1 1  
Long-term debt | CAD             CAD 210.0    
Long-term debt excluding debentures                  
Derivative instruments                  
Long-term debt           $ (15.8)   $ (15.7)  
Senior secured term loan, due 2021 | Long-term debt excluding debentures                  
Derivative instruments                  
Long-term debt           $ 473.2   447.9  
Adjusted Eurodollar Rate                  
Derivative instruments                  
Minimum percentage of variable rate base   1.00%              
Applicable margin (as a percent)   3.75%              
Gas purchase agreements | Ontario project                  
Derivative instruments                  
Notional amount, energy (in gigajoules: Ontario, in Mmbtu: Orlando) | MMBTU     2,900,000            
Gas purchase agreements | Morris Project                  
Derivative instruments                  
Notional amount, energy (in gigajoules: Ontario, in Mmbtu: Orlando) | MMBTU       450,000          
Expected uncontracted gas requirements for 2015 | Ontario project                  
Derivative instruments                  
Percentage of requirements whose price is fixed by derivative       100.00%          
Expected uncontracted gas requirements for 2016 | Ontario project                  
Derivative instruments                  
Percentage of requirements whose price is fixed by derivative       35.00%          
Expected uncontracted gas requirements for 2017 | Ontario project                  
Derivative instruments                  
Percentage of requirements whose price is fixed by derivative       30.00%          
Natural gas swaps                  
Derivative instruments                  
Notional amount, energy (in gigajoules: Ontario, in Mmbtu: Orlando) | MMBTU       6,700,000   2,800,000      
Natural gas swaps | Derivative instruments not designated as cash flow hedges                  
Derivative instruments                  
Gain (Loss) on Sale of Derivatives       $ 2.0 $ 12.0        
Natural gas swaps during remainder of 2014 | Orlando project                  
Derivative instruments                  
Notional amount, energy (in gigajoules: Ontario, in Mmbtu: Orlando) | MMBTU       7,700,000          
Percentage of the entity's share in required natural gas purchases hedge       95.00%          
Interest rate swaps                  
Derivative instruments                  
Minimum fixed interest rate (as a percent) 4.75% 4.75%              
Notional amount           $ 302.3   228.9  
Maximum fixed interest rate (as a percent) 4.91% 4.91%              
Interest rate swaps | Derivative instruments not designated as cash flow hedges                  
Derivative instruments                  
Gain (Loss) on Sale of Derivatives       $ 0.6 $ (1.0)        
Interest rate swaps | Adjusted Eurodollar Rate                  
Derivative instruments                  
Notional amount $ 199.0 $ 199.0           140.4  
Aggregate principal amount of debt               $ 447.9  
Interest rate swaps | Adjusted Eurodollar Rate | Senior secured term loan, due 2021 | Long-term debt excluding debentures                  
Derivative instruments                  
Notional amount 199.0 199.0              
Aggregate principal amount of debt $ 600.0 $ 600.0              
Interest rate swaps | Adjusted Eurodollar Rate | Derivative instruments not designated as cash flow hedges                  
Derivative instruments                  
Swaption interest rate (as a percent) 1.16% 1.16%              
Interest rate swaps | Adjusted Eurodollar Below One Percent                  
Derivative instruments                  
Swaption all in one interest rate (as a percent) 4.75% 4.75%              
Interest rate swaps | Minimum | Adjusted Eurodollar Rate                  
Derivative instruments                  
Minimum percentage of variable rate base 1.00%                
Interest rate swaps | Piedmont                  
Derivative instruments                  
Long-term debt                 $ 68.5
Interest rate swaps | Swaption interest rate until February 15, 2015 | Cadillac Project                  
Derivative instruments                  
Swaption interest rate (as a percent)             6.00% 6.00%  
Interest rate swaps | Swaption interest rate from February 16, 2015 to February 15, 2019 | Cadillac Project                  
Derivative instruments                  
Swaption interest rate (as a percent)             6.10% 6.10%  
Interest rate swaps | Swaption interest rate from February 16, 2019 to February 15, 2023 | Cadillac Project                  
Derivative instruments                  
Swaption interest rate (as a percent)             6.30% 6.30%  
Interest rate swaps | Swaption interest rate after February 15, 2023 | Cadillac Project                  
Derivative instruments                  
Swaption interest rate (as a percent)             6.40% 6.40%  
Interest rate swaps | Swaption interest rate until February 29, 2016 | Piedmont                  
Derivative instruments                  
Swaption interest rate (as a percent)             1.70% 1.70%  
Applicable margin, low end of range (as a percent)             3.50% 3.50%  
Applicable margin, high end of range (as a percent)             3.80% 3.80%  
Interest rate swaps | Swaption interest rate from February, 2016 to November, 2017 | Piedmont                  
Derivative instruments                  
Swaption interest rate (as a percent)             4.47% 4.47%  
Applicable margin of derivative (as a percent)             4.00% 4.00%  
Swaption all in one interest rate (as a percent)             8.50% 8.50%  
Interest rate swaps | Swaption interest rate from November, 2017 to November, 2030 | Piedmont                  
Derivative instruments                  
Swaption interest rate (as a percent)             4.47% 4.47%