| Fair Value, Measurement Inputs, Disclosure [Text Block] |
The following assets and liabilities are measured at fair value: | | | | | | | | | | | | | | | | | | March 31, 2012 | | Level 1 | | Level 2 | | Level 3 | | Total | | (Thousands of Dollars) | Other current assets: | | | | | | | | Product imbalances | $ | 1,661 |
| | $ | — |
| | $ | — |
| | $ | 1,661 |
| Commodity derivatives | 21,880 |
| | 329 |
| | — |
| | 22,209 |
| Other long-term assets, net: | | | | | | | | Commodity derivatives | — |
| | 5,377 |
| | — |
| | 5,377 |
| Interest rate swaps | — |
| | 581 |
| | — |
| | 581 |
| Accrued liabilities: | | | | | | | | Product imbalances | (200 | ) | | — |
| | — |
| | (200 | ) | Commodity derivatives | (13,692 | ) | | (24,500 | ) | | — |
| | (38,192 | ) | Interest rate swaps | — |
| | (9,796 | ) | | — |
| | (9,796 | ) | Other long-term liabilities: | | | | | | | | Commodity derivatives | — |
| | (6,539 | ) | | — |
| | (6,539 | ) | Interest rate swaps | — |
| | (11,221 | ) | | — |
| | (11,221 | ) | Total | $ | 9,649 |
| | $ | (45,769 | ) | | $ | — |
| | $ | (36,120 | ) |
| | | | | | | | | | | | | | | | | | December 31, 2011 | | Level 1 | | Level 2 | | Level 3 | | Total | | (Thousands of Dollars) | Other current assets: | | | | | | | | Product imbalances | $ | 2,117 |
| | $ | — |
| | $ | — |
| | $ | 2,117 |
| Commodity derivatives | 10,282 |
| | 1,830 |
| | — |
| | 12,112 |
| Other long-term assets, net: | | | | | | | | Commodity derivatives | — |
| | 27,084 |
| | — |
| | 27,084 |
| Interest rate swaps | — |
| | 2,335 |
| | — |
| | 2,335 |
| Accrued liabilities: | | | | | | | | Product imbalances | (1,469 | ) | | — |
| | — |
| | (1,469 | ) | Commodity derivatives | (5,424 | ) | | — |
| | — |
| | (5,424 | ) | Interest rate swaps | — |
| | (22,009 | ) | | — |
| | (22,009 | ) | Other long-term liabilities: | | | | | | | | Interest rate swaps | — |
| | (27,190 | ) | | — |
| | (27,190 | ) | Total | $ | 5,506 |
| | $ | (17,950 | ) | | $ | — |
| | $ | (12,444 | ) |
|
| Fair Value and Carrying Value of Debt [Text Block] |
The estimated fair value and carrying amount of our debt was as follows: | | | | | | | | | | March 31, 2012 | | December 31, 2011 | | (Thousands of Dollars) | Fair value | $ | 2,575,496 |
| | $ | 2,377,565 |
| Carrying amount | $ | 2,521,412 |
| | $ | 2,293,030 |
|
|