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Retirement Benefits | 6 Months Ended
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Jun. 30, 2017
Retirement Benefits [Abstract] |
Retirement Benefits | Retirement Benefits The components of the net periodic pension benefit (credit) cost were as follows:
| Three Months Ended |  | Six Months Ended
| June 30, 2017 |  | June 30, 2016 |  | June 30, 2017 |  | June 30, 2016
| (Dollars in thousands)
Service cost | $ | 3,267 |  |  | $ | 3,321 |  |  | $ | 6,435 |  |  | $ | 6,634 |
Interest cost | 6,362 |  |  | 6,444 |  |  | 12,632 |  |  | 12,878 |
Expected return on plan assets | (15,713 | ) |  | (14,583 | ) |  | (31,426 | ) |  | (29,166 | )
Amortization of prior service cost | 80 |  |  | 151 |  |  | 160 |  |  | 302 |
Amortization of actuarial losses | 1,854 |  |  | 2,084 |  |  | 3,707 |  |  | 4,167 |
Special termination benefits | — |  |  | 2,900 |  |  | — |  |  | 2,900 |
Curtailment loss | — |  |  | 180 |  |  | — |  |  | 180 |
Net periodic benefit (credit) cost | $ | (4,150 | ) |  | $ | 497 |  |  | $ | (8,492 | ) |  | $ | (2,105 | )
The components of the net periodic other postretirement benefit credit were as follows:
| Three Months Ended |  | Six Months Ended
| June 30, 2017 |  | June 30, 2016 |  | June 30, 2017 |  | June 30, 2016
| (Dollars in thousands)
Service cost | $ | 34 |  |  | $ | 69 |  |  | $ | 70 |  |  | $ | 136 |
Interest cost | 176 |  |  | 253 |  |  | 352 |  |  | 507 |
Amortization of prior service credit | (854 | ) |  | (850 | ) |  | (1,707 | ) |  | (1,700 | )
Amortization of actuarial gains | (136 | ) |  | (170 | ) |  | (275 | ) |  | (288 | )
Net periodic benefit credit | $ | (780 | ) |  | $ | (698 | ) |  | $ | (1,560 | ) |  | $ | (1,345 | )

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- References No definition available. + Details
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- Definition The entire disclosure for pension and other postretirement benefits. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -URI http://asc.fasb.org/topic&trid=2235017 + Details
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