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Retirement Benefits | 9 Months Ended
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Sep. 30, 2017
Retirement Benefits [Abstract] |
Retirement Benefits | Retirement Benefits The components of the net periodic pension benefit credit were as follows:
| Three Months Ended |  | Nine Months Ended
| Sept. 30, 2017 |  | Sept. 30, 2016 |  | Sept. 30, 2017 |  | Sept. 30, 2016
| (Dollars in thousands)
Service cost | $ | 3,532 |  |  | $ | 2,950 |  |  | $ | 9,967 |  |  | $ | 9,584 |
Interest cost | 6,482 |  |  | 6,473 |  |  | 19,114 |  |  | 19,351 |
Expected return on plan assets | (15,832 | ) |  | (14,653 | ) |  | (47,258 | ) |  | (43,819 | )
Amortization of prior service cost | 75 |  |  | 113 |  |  | 235 |  |  | 415 |
Amortization of actuarial losses | 1,501 |  |  | 2,326 |  |  | 5,208 |  |  | 6,493 |
Special termination benefits | — |  |  | — |  |  | — |  |  | 2,900 |
Curtailment loss | — |  |  | — |  |  | — |  |  | 180 |
Net periodic benefit credit | $ | (4,242 | ) |  | $ | (2,791 | ) |  | $ | (12,734 | ) |  | $ | (4,896 | )
The components of the net periodic other postretirement benefit credit were as follows:
| Three Months Ended |  | Nine Months Ended
| Sept. 30, 2017 |  | Sept. 30, 2016 |  | Sept. 30, 2017 |  | Sept. 30, 2016
| (Dollars in thousands)
Service cost | $ | 9 |  |  | $ | 52 |  |  | $ | 79 |  |  | $ | 188 |
Interest cost | 168 |  |  | 230 |  |  | 520 |  |  | 737 |
Amortization of prior service credit | (857 | ) |  | (816 | ) |  | (2,564 | ) |  | (2,516 | )
Amortization of actuarial gains | (172 | ) |  | (187 | ) |  | (447 | ) |  | (475 | )
Net periodic benefit credit | $ | (852 | ) |  | $ | (721 | ) |  | $ | (2,412 | ) |  | $ | (2,066 | )

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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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