| Schedule of Segment Reporting Information, by Segment [Table Text Block] |
Results of operations for the reportable segments were as follows: | | | | | | | | | | | | | | | | | | Three Months Ended June 30, | | Six Months Ended June 30, | | 2016 | | 2015 | | 2016 | | 2015 | | (Thousands of Dollars) | Revenues: | | | | | | | | Pipeline | $ | 121,575 |
| | $ | 122,210 |
| | $ | 240,448 |
| | $ | 246,635 |
| Storage: | | | | | | | | Third parties | 146,367 |
| | 150,812 |
| | 292,751 |
| | 294,897 |
| Intersegment | 5,507 |
| | 6,830 |
| | 11,522 |
| | 13,079 |
| Total storage | 151,874 |
| | 157,642 |
| | 304,273 |
| | 307,976 |
| Fuels Marketing | 169,862 |
| | 297,589 |
| | 310,308 |
| | 584,023 |
| Consolidation and intersegment eliminations | (5,507 | ) | | (6,830 | ) | | (11,522 | ) | | (13,079 | ) | Total revenues | $ | 437,804 |
| | $ | 570,611 |
| | $ | 843,507 |
| | $ | 1,125,555 |
| | | | | | | | | Operating income: | | | | | | | | Pipeline | $ | 63,552 |
| | $ | 64,820 |
| | $ | 127,817 |
| | $ | 133,460 |
| Storage | 51,063 |
| | 53,751 |
| | 108,076 |
| | 101,729 |
| Fuels marketing | 1,392 |
| | 2,650 |
| | 619 |
| | 12,575 |
| Consolidation and intersegment eliminations | 1 |
| | (1 | ) | | 1 |
| | 42 |
| Total segment operating income | 116,008 |
| | 121,220 |
| | 236,513 |
| | 247,806 |
| General and administrative expenses | 22,657 |
| | 26,693 |
| | 46,442 |
| | 51,746 |
| Other depreciation and amortization expense | 2,134 |
| | 2,122 |
| | 4,289 |
| | 4,374 |
| Total operating income | $ | 91,217 |
| | $ | 92,405 |
| | $ | 185,782 |
| | $ | 191,686 |
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| Reconciliation of Assets from Segment to Consolidated [Table Text Block] |
Total assets by reportable segment were as follows: | | | | | | | | | | June 30,
2016 | | December 31,
2015 | | (Thousands of Dollars) | Pipeline | $ | 2,004,850 |
| | $ | 2,014,098 |
| Storage | 2,466,104 |
| | 2,476,389 |
| Fuels marketing | 140,150 |
| | 156,866 |
| Total segment assets | 4,611,104 |
| | 4,647,353 |
| Other partnership assets | 444,115 |
| | 478,172 |
| Total consolidated assets | $ | 5,055,219 |
| | $ | 5,125,525 |
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