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Accumulated Other Comprehensive Loss Accumulated Other Comprehensive Loss (Tables) | 12 Months Ended
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Dec. 31, 2019
Accumulated Other Comprehensive Loss [Abstract] |
Reclassification out of Accumulated Other Comprehensive Income [Table Text Block] | The following table details the reclassifications out of accumulated other comprehensive loss by component for the years ended December 31 (dollars in thousands):
|  | Amounts Reclassified from Accumulated Other Comprehensive Loss |  |
Details about Accumulated Other Comprehensive Loss Components |  | 2019 |  | 2018 |  | 2017 |  | Affected Line Item in Statement of Income
Amortization of defined benefit pension items |  |  |  |  |  |  |  |
Amortization of net prior service cost |  | $ | (794 | ) |  | $ | (904 | ) |  | $ | (4,381 | ) |  | (a)
Amortization of net loss |  | 17,074 |  |  | (15,554 | ) |  | 36,833 |  |  | (a)
Adjustment due to effects of regulation |  | (19,309 | ) |  | 18,947 |  |  | (33,255 | ) |  | (a)
|  | (3,029 | ) |  | 2,489 |  |  | (803 | ) |  | Total before tax
|  | 636 |  |  | (523 | ) |  | 281 |  |  | Tax benefit (expense)
|  | $ | (2,393 | ) |  | $ | 1,966 |  |  | $ | (522 | ) |  | Net of tax
(a) These accumulated other comprehensive loss components are included in the computation of net periodic pension cost (see Note 11 for additional details).
Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block] | Accumulated other comprehensive loss, net of tax, consisted of the following as of December 31 (dollars in thousands):
| 2019 |  | 2018
Unfunded benefit obligation for pensions and other postretirement benefit plans - net of taxes of $2,727 and $2,091, respectively | $ | 10,259 |  |  | $ | 7,866 |

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- Definition Accumulated Other Comprehensive Loss [Abstract] + References No definition available. + Details
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- Definition Tabular disclosure of information about items reclassified out of accumulated other comprehensive income (loss). + References No definition available. + Details
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- Definition Tabular disclosure of the components of accumulated other comprehensive income (loss). + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 14A -URI http://asc.fasb.org/extlink&oid=118930883&loc=SL7669686-108580 + Details
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