| Schedule of Changes in Current Assets and Liabilities [Text Block] |
Changes in current assets and current liabilities were as follows: | | | | | | | | | | | | | | Year Ended December 31, | | 2015 | | 2014 | | 2013 | | (Thousands of Dollars) | Decrease (increase) in current assets: | | | | | | Accounts receivable | $ | 67,257 |
| | $ | 72,298 |
| | $ | 107,209 |
| Receivable from related parties | — |
| | 50,918 |
| | 58,692 |
| Inventories | 16,776 |
| | 82,075 |
| | 31,975 |
| Other current assets | 4,414 |
| | 3,785 |
| | 26,139 |
| Increase (decrease) in current liabilities: | | | | | | Accounts payable | (32,152 | ) | | (153,671 | ) | | (96,330 | ) | Payable to related party | (872 | ) | | 837 |
| | 6,922 |
| Accrued interest payable | 941 |
| | 303 |
| | 9,370 |
| Accrued liabilities | (7,834 | ) | | 22,980 |
| | (32,452 | ) | Taxes other than income tax | (1,522 | ) | | 4,341 |
| | (87 | ) | Income tax payable | 3,551 |
| | (1,448 | ) | | 1,338 |
| Changes in current assets and current liabilities | $ | 50,559 |
| | $ | 82,418 |
| | $ | 112,776 |
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| Schedule of Supplemental Cash Flow Information [Text Block] |
Cash flows related to interest and income taxes were as follows: | | | | | | | | | | | | | | Year Ended December 31, | | 2015 | | 2014 | | 2013 | | (Thousands of Dollars) | Cash paid for interest, net of amount capitalized | $ | 133,388 |
| | $ | 129,377 |
| | $ | 113,805 |
| Cash paid for income taxes, net of tax refunds received | $ | 9,971 |
| | $ | 6,699 |
| | $ | 11,386 |
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