| Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block] |
The balance of and changes in the components included in AOCI were as follows: | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Three Months Ended June 30, | | 2021 | | 2020 | | Foreign Currency Translation | | Cash Flow Hedges | | Pension and Other Postretirement Benefits | | Total | | Foreign Currency Translation | | Cash Flow Hedges | | Pension and Other Postretirement Benefits | | Total | | (Thousands of Dollars) | | Balance as of March 31 | $ | (41,405) | | | $ | (40,802) | | | $ | (12,329) | | | $ | (94,536) | | | $ | (50,600) | | | $ | (45,307) | | | $ | (8,302) | | | $ | (104,209) | | Other comprehensive income (loss): | | | | | | | | | | | | | | | | Other comprehensive income (loss) before reclassification adjustments | 1,094 | | | — | | | — | | | 1,094 | | | 2,638 | | | (461) | | | — | | | 2,177 | | Net gain on pension costs reclassified into other income, net | — | | | — | | | (187) | | | (187) | | | — | | | — | | | (305) | | | (305) | | Net loss on cash flow hedges reclassified into interest expense, net | — | | | 1,335 | | | — | | | 1,335 | | | — | | | 878 | | | — | | | 878 | | Other | — | | | — | | | 2 | | | 2 | | | — | | | — | | | 4 | | | 4 | | Other comprehensive income (loss) | 1,094 | | | 1,335 | | | (185) | | | 2,244 | | | 2,638 | | | 417 | | | (301) | | | 2,754 | | | Balance as of June 30 | $ | (40,311) | | | $ | (39,467) | | | $ | (12,514) | | | $ | (92,292) | | | $ | (47,962) | | | $ | (44,890) | | | $ | (8,603) | | | $ | (101,455) | |
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Six Months Ended June 30, | | 2021 | | 2020 | | Foreign Currency Translation | | Cash Flow Hedges | | Pension and Other Postretirement Benefits | | Total | | Foreign Currency Translation | | Cash Flow Hedges | | Pension and Other Postretirement Benefits | | Total | | (Thousands of Dollars) | | Balance as of January 1 | $ | (42,362) | | | $ | (42,150) | | | $ | (12,144) | | | $ | (96,656) | | | $ | (43,772) | | | $ | (16,124) | | | $ | (8,000) | | | $ | (67,896) | | Other comprehensive income (loss): | | | | | | | | | | | | | | | | | Other comprehensive income (loss) before reclassification adjustments | 2,051 | | | — | | | — | | | 2,051 | | | (4,190) | | | (30,291) | | | — | | | (34,481) | | Net gain on pension costs reclassified into other income, net | — | | | — | | | (374) | | | (374) | | | — | | | — | | | (610) | | | (610) | | Net loss on cash flow hedges reclassified into interest expense, net | — | | | 2,683 | | | — | | | 2,683 | | | — | | | 1,525 | | | — | | | 1,525 | | Other | — | | | — | | | 4 | | | 4 | | | — | | | — | | | 7 | | | 7 | | | Other comprehensive income (loss) | 2,051 | | | 2,683 | | | (370) | | | 4,364 | | | (4,190) | | | (28,766) | | | (603) | | | (33,559) | | | Balance as of June 30 | $ | (40,311) | | | $ | (39,467) | | | $ | (12,514) | | | $ | (92,292) | | | $ | (47,962) | | | $ | (44,890) | | | $ | (8,603) | | | $ | (101,455) | |
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| Distributions Made to Limited Partner, by Distribution [Table Text Block] |
Distributions on our Series A, B and C Preferred Units are payable out of any legally available funds, accrue and are cumulative from the original issuance dates, and are payable on the 15th day (or next business day) of each of March, June, September and December of each year to holders of record on the first business day of each payment month as follows (until the distribution rate changes to a floating rate): | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Units | | | | | | | | | | Fixed Distribution Rate Per Unit Per Quarter | | Fixed Distribution Per Quarter | | Date at Which Distribution Rate Becomes Floating | | | | | | | | | | | | | (Thousands of Dollars) | | | | Series A Preferred Units | | | | | | | | | | $ | 0.53125 | | | $ | 4,813 | | | December 15, 2021 | | Series B Preferred Units | | | | | | | | | | $ | 0.47657 | | | $ | 7,339 | | | June 15, 2022 | | Series C Preferred Units | | | | | | | | | | $ | 0.56250 | | | $ | 3,881 | | | December 15, 2022 |
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| Distributions Made to Limited Partner, by Distribution [Table Text Block] |
The following table summarizes information about quarterly cash distributions declared for our common limited partners: | | | | | | | | | | | | | | | | | | | | | | | | | | | | Quarter Ended | | Cash Distributions Per Unit | | Total Cash Distributions | | Record Date | | Payment Date | | | | | (Thousands of Dollars) | | | | | | | | | | | | | | | June 30, 2021 | | $ | 0.40 | | | $ | 43,814 | | | August 6, 2021 | | August 12, 2021 | | March 31, 2021 | | $ | 0.40 | | | $ | 43,834 | | | May 10, 2021 | | May 14, 2021 | | December 31, 2020 | | $ | 0.40 | | | $ | 43,787 | | | February 8, 2021 | | February 12, 2021 |
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