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Retirement Plans, Weighted Average Assumptions Used to Determine Net Periodic Benefit Cost, Pension Benefits (Details) | 2 Months Ended | 9 Months Ended | 12 Months Ended
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Mar. 31, 2018 | Feb. 14, 2018 | Dec. 31, 2018 | Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Pension Benefits [Member] |  |  |  |  |  |  |  |
Weighted average assumptions used to determine net periodic benefit cost [Abstract] |  |  |  |  |  |  |  |
Discount rate | [1] |  |  |  | 3.50% |  | 4.40% | 3.70%
Expected long-term rate of return on plan assets |  |  |  |  | 6.75% |  | 7.00% | 7.00%
Pension Benefits [Member] | Higman [Member] |  |  |  |  |  |  |  |
Weighted average assumptions used to determine net periodic benefit cost [Abstract] |  |  |  |  |  |  |  |
Discount rate |  | 4.02% | 4.13% | 4.40% | 3.10% | [1] |  |
SERP [Member] |  |  |  |  |  |  |  |
Weighted average assumptions used to determine net periodic benefit cost [Abstract] |  |  |  |  |  |  |  |
Discount rate |  |  |  |  | 3.50% |  | 4.40% | 3.70%
Expected long-term rate of return on plan assets |  |  |  |  | 0.00% |  | 0.00% | 0.00%
Rate of compensation increase |  |  |  |  | 0.00% |  | 0.00% | 0.00%
[1] | The 2020 discount rate for benefit cost is 3.5% for the Kirby pension plan and 3.1% for the Higman pension plan. The 2018 discount rate for benefit cost for the Higman pension plan was changed from 4.13% as of February 14, 2018 and 4.02% as of March 31, 2018 to 4.40% as of December 31, 2018.

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- Definition Weighted average rate for present value of future retirement benefits cash flows, used to determine net periodic benefit cost of defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (k)(1) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 + Details
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- Definition Weighted average rate of return on plan assets, reflecting average rate of earnings expected on existing plan assets and expected contributions, used to determine net periodic benefit cost of defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (k)(3) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 8 -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e2919-114920 + Details
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- Definition Weighted average rate of compensation increase used to determine net periodic benefit cost of defined benefit plan. Plan includes, but is not limited to, pay-related defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (k)(2) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 + Details
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