| Schedule of Segment Reporting Information, by Segment [Table Text Block] |
Results of operations for the reportable segments were as follows: | | | | | | | | | | | | | | | | | | Three Months Ended September 30, | | Nine Months Ended September 30, | | 2016 | | 2015 | | 2016 | | 2015 | | (Thousands of Dollars) | Revenues: | | | | | | | | Pipeline | $ | 122,481 |
| | $ | 131,395 |
| | $ | 362,929 |
| | $ | 378,030 |
| Storage: | | | | | | | | Third parties | 152,746 |
| | 155,475 |
| | 445,497 |
| | 450,372 |
| Intersegment | 5,021 |
| | 6,628 |
| | 16,543 |
| | 19,707 |
| Total storage | 157,767 |
| | 162,103 |
| | 462,040 |
| | 470,079 |
| Fuels marketing | 166,191 |
| | 206,696 |
| | 476,499 |
| | 790,719 |
| Consolidation and intersegment eliminations | (5,021 | ) | | (6,628 | ) | | (16,543 | ) | | (19,707 | ) | Total revenues | $ | 441,418 |
| | $ | 493,566 |
| | $ | 1,284,925 |
| | $ | 1,619,121 |
| | | | | | | | | Operating income (loss): | | | | | | | | Pipeline | $ | 58,922 |
| | $ | 68,536 |
| | $ | 186,739 |
| | $ | 201,996 |
| Storage | 58,420 |
| | 59,986 |
| | 166,496 |
| | 161,715 |
| Fuels marketing | (337 | ) | | (1,819 | ) | | 282 |
| | 10,756 |
| Consolidation and intersegment eliminations | (1 | ) | | (1 | ) | | — |
| | 41 |
| Total segment operating income | 117,004 |
| | 126,702 |
| | 353,517 |
| | 374,508 |
| General and administrative expenses | 26,957 |
| | 23,679 |
| | 73,399 |
| | 75,425 |
| Other depreciation and amortization expense | 2,093 |
| | 2,029 |
| | 6,382 |
| | 6,403 |
| Total operating income | $ | 87,954 |
| | $ | 100,994 |
| | $ | 273,736 |
| | $ | 292,680 |
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| Reconciliation of Assets from Segment to Consolidated [Table Text Block] |
Total assets by reportable segment were as follows: | | | | | | | | | | September 30,
2016 | | December 31,
2015 | | (Thousands of Dollars) | Pipeline | $ | 2,014,710 |
| | $ | 2,014,098 |
| Storage | 2,462,597 |
| | 2,476,389 |
| Fuels marketing | 143,438 |
| | 156,866 |
| Total segment assets | 4,620,745 |
| | 4,647,353 |
| Other partnership assets | 369,673 |
| | 478,172 |
| Total consolidated assets | $ | 4,990,418 |
| | $ | 5,125,525 |
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