|
Accounting for derivative instruments and hedging activities (Details 2)
In Thousands, unless otherwise specified |
Dec. 31, 2012
Natural gas swaps
MMBTU
|
Dec. 31, 2011
Natural gas swaps
MMBTU
|
Dec. 31, 2012
Gas purchase agreements
gigajoule
|
Dec. 31, 2012
Interest rate swaps
USD ($)
|
Dec. 31, 2011
Interest rate swaps
USD ($)
|
Dec. 31, 2012
Currency forward
CAD
|
Dec. 31, 2011
Currency forward
CAD
|
|---|---|---|---|---|---|---|---|
| Derivative instruments | |||||||
| Volume of forecasted transactions | 10,640,000 | 14,140,000 | 49,810,000 | ||||
| Volume of forecasted transactions, (in dollars) | $ 140,154 | $ 52,711 | 176,550 | 312,533 |