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Accumulated Other Comprehensive Loss Accumulated Other Comprehensive Loss (Tables) | 9 Months Ended
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Sep. 30, 2018
Accumulated Other Comprehensive Loss [Abstract] |
Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block] | Accumulated other comprehensive loss, net of tax, consisted of the following as of September 30, 2018 and December 31, 2017 (dollars in thousands):
| September 30, |  | December 31,
| 2018 |  | 2017
Unfunded benefit obligation for pensions and other postretirement benefit plans - net of taxes of $2,451 and $4,356, respectively (a) | $ | 9,220 |  |  | $ | 8,090 |
(a) | Effective January 1, 2018, the Company adopted ASU No. 2018-02. As a result of the adoption of this new standard, $1.7 million in excess tax benefits was reclassified from accumulated other comprehensive loss to retained earnings. See Note 2 for additional discussion of the adoption of this standard.
Reclassification out of Accumulated Other Comprehensive Income [Table Text Block] | The following table details the reclassifications out of accumulated other comprehensive loss to net income by component for the three and nine months ended September 30 (dollars in thousands).
|  | Amounts Reclassified from Accumulated Other Comprehensive Loss |  |
|  | Three months ended September 30, |  | Nine months ended September 30, |  |
Details about Accumulated Other Comprehensive Loss Components |  | 2018 |  | 2017 |  | 2018 |  | 2017 |  | Affected Line Item in Statement of Income
Amortization of defined benefit pension items |  |  |  |  |  |  |  |
Amortization of net prior service cost |  | $ | (228 | ) |  | $ | (300 | ) |  | $ | (684 | ) |  | $ | (898 | ) |  | (a)
Amortization of net loss |  | 2,962 |  |  | 3,637 |  |  | $ | 8,952 |  |  | $ | 10,913 |  |  | (a)
Adjustment due to effects of regulation |  | (2,476 | ) |  | (3,057 | ) |  | (7,493 | ) |  | (9,172 | ) |  | (a)
|  | 258 |  |  | 280 |  |  | 775 |  |  | 843 |  |  | Total before tax
|  | (54 | ) |  | (98 | ) |  | (163 | ) |  | (295 | ) |  | Tax expense
|  | $ | 204 |  |  | $ | 182 |  |  | $ | 612 |  |  | $ | 548 |  |  | Net of tax
(a) | These accumulated other comprehensive loss components are included in the computation of net periodic pension cost (see Note 6 for additional details).

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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://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 14A -URI http://asc.fasb.org/extlink&oid=84228862&loc=SL7669686-108580 + Details
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