Natural Gas Basis Contracts That are Not Designated for Hedge Accounting (Details) (Basis contracts [Member], USD $)
| Sep. 30, 2011 |
|---|
| Natural gas basis contracts not designated for hedge accounting [Abstract] | |
| Derivative Liability, Fair Value, Total | $ (12,000,000) |
Rocky Mountains [Member] | October 2011 - December 2011 [Member] | |
| Natural gas basis contracts not designated for hedge accounting [Abstract] | |
| Volume in MMMBtus | 1,320 |
| Weighted Average Differential | (0.95) |
Rocky Mountains [Member] | January 2012 - December 2012 [Member] | |
| Natural gas basis contracts not designated for hedge accounting [Abstract] | |
| Volume in MMMBtus | 4,920 |
| Weighted Average Differential | (0.91) |
Mid-Continent [Member] | October 2011 - December 2011 [Member] | |
| Natural gas basis contracts not designated for hedge accounting [Abstract] | |
| Volume in MMMBtus | 4,290 |
| Weighted Average Differential | (0.55) |
Mid-Continent [Member] | January 2012 - December 2012 [Member] | |
| Natural gas basis contracts not designated for hedge accounting [Abstract] | |
| Volume in MMMBtus | 18,300 |
| Weighted Average Differential | (0.55) |
October 2011 - December 2011 [Member] | |
| Natural gas basis contracts not designated for hedge accounting [Abstract] | |
| Derivative Liability, Fair Value, Total | (3,000,000) |
January 2012 - December 2012 [Member] | |
| Natural gas basis contracts not designated for hedge accounting [Abstract] | |
| Derivative Liability, Fair Value, Total | $ (9,000,000) |