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Retirement plans and postretirement benefits (Tables) | 6 Months Ended | 12 Months Ended
--- | --- | ---
Jun. 30, 2018 | Dec. 31, 2017
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |
Amounts Recognized In Other Comprehensive Income Retirement Plans |  | The mark-to-market gain in 2017 was the result of better than expected returns on assets, partially offset by an unfavorable change to the discount rate. The mark-to-market gain in 2016 was the result of better than expected returns on plan assets and favorable changes to the mortality tables, partially offset by unfavorable changes to the discount rate.
Reconciliation Of Pension Plans' Benefit Obligations, Fair Value Of Assets Retirement Plans |  |
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
|  | As of December 31, 2017 |  | As of December 31, 2016 |
|  | U.S. |  | Foreign |  | U.S. |  | Foreign |
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
|  | (Dollars in thousands) |
Changes in Benefit Obligation: |  |  |  |  |  |  |  |  |
Net Benefit Obligation at beginning of period |  | $ | 140,230 |  | $ | 18,237 |  | $ | 142,126 |  | $ | 18,271 |
Service cost |  | 1,305 |  | 710 |  | 1,325 |  | 698 |
Interest cost |  | 5,352 |  | 199 |  | 5,744 |  | 243 |
Participant contributions |  | — |  | 252 |  | — |  | 256 |
Plan amendments / curtailments |  | — |  | — |  | — |  | (122 | )
Foreign currency exchange changes |  | — |  | 1,069 |  | — |  | (527 | )
Actuarial loss (gain) |  | 3,212 |  | 63 |  | 1,293 |  | (18 | )
Benefits paid |  | (10,353 | ) | (123 | ) | (10,258 | ) | (564 | )
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Net benefit obligation at end of period |  | $ | 139,746 |  | $ | 20,407 |  | $ | 140,230 |  | $ | 18,237 |
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Changes in Plan Assets: |  |  |  |  |  |  |  |  |
Fair value of plan assets at beginning of period |  | $ | 100,905 |  | $ | 11,871 |  | $ | 93,897 |  | $ | 11,293 |
Actual return on plan assets |  | 12,620 |  | 415 |  | 8,556 |  | 378 |
Foreign currency exchange rate changes |  | — |  | 545 |  | — |  | (346 | )
Employer contributions |  | 6,673 |  | 658 |  | 8,710 |  | 854 |
Participant contributions |  | — |  | 252 |  | — |  | 256 |
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Benefits paid |  | (10,353 | ) | (123 | ) | (10,258 | ) | (564 | )
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Fair value of plan assets at end of period |  | $ | 109,845 |  | $ | 13,618 |  | $ | 100,905 |  | $ | 11,871 |
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Funded status (underfunded): |  | $ | (29,901 | ) | $ | (6,789 | ) | $ | (39,325 | ) | $ | (6,366 | )
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Amounts recognized in accumulated other comprehensive loss: |  |  |  |  |  |  |  |  |
Prior service credit |  | $ | — |  | $ | — |  | $ | — |  | $ | — |
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Amounts recognized in the statement of financial position: |  |  |  |  |  |  |  |  |
Non-current assets |  | $ | — |  | $ | — |  | $ | — |  | $ | — |
Current liabilities |  | (433 | ) | (146 | ) | (435 | ) | (128 | )
Non-current liabilities |  | (29,468 | ) | (6,643 | ) | (38,890 | ) | (6,238 | )
Net amount recognized |  | $ | (29,901 | ) | $ | (6,789 | ) | $ | (39,325 | ) | $ | (6,366 | )
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Fair Asset Values Of Plan Assets |  | The fair value of the plan assets by category is summarized below (dollars in thousands):
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
|  | As of December 31, 2017 |
|  | Level 1 |  | Level 2 |  | Level 3 |  | Total |
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
U.S. Plan Assets |  |  |  |  |  |  |  |  |
Cash and cash equivalents |  | $ | 2,094 |  | $ | — |  | $ | — |  | $ | 2,094 |
Collective trusts |  | — |  | 107,751 |  | — |  | 107,751 |
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Total |  | $ | 2,094 |  | $ | 107,751 |  | $ | — |  | $ | 109,845 |
International Plan Assets |  |  |  |  |  |  |  |  |
Foreign government bonds |  | $ | — |  | $ | 831 |  | $ | — |  | $ | 831 |
Fixed insurance contracts |  | — |  | — |  | 12,787 |  | 12,787 |
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Total |  | $ | — |  | $ | 831 |  | $ | 12,787 |  | $ | 13,618 |
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
|  | As of December 31, 2016 |
|  | Level 1 |  | Level 2 |  | Level 3 |  | Total |
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
U.S. Plan Assets |  |  |  |  |  |  |  |  |
Cash and cash equivalents |  | $ | 1,502 |  | $ | — |  | $ | — |  | $ | 1,502 |
Collective trusts |  | — |  | 99,403 |  | — |  | 99,403 |
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Total |  | $ | 1,502 |  | $ | 99,403 |  | $ | — |  | $ | 100,905 |
International Plan Assets |  |  |  |  |  |  |  |  |
Foreign government bonds |  | $ | — |  | $ | 729 |  | $ | — |  | $ | 729 |
Fixed insurance contracts |  | — |  | — |  | 11,142 |  | 11,142 |
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Total |  | $ | — |  | $ | 729 |  | $ | 11,142 |  | $ | 11,871 |
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Fair Value Hierarchy, Assets At Fair Value |  | The following table presents the changes for those financial instruments classified within Level 3 of the valuation hierarchy for international plan pension assets for the years ended December 31, 2016 and 2017 (dollars in thousands):
​ | ​ | ​ | ​
|  | Fixed insurance contracts |
​ | ​ | ​ | ​
Balance at December 31, 2015 |  | $ | 10,453 |
Gain / contributions / currency impact |  | 707 |
Distributions |  | (18 | )
​ | ​ | ​ | ​
Balance at December 31, 2016 |  | 11,142 |
Gain / contributions / currency impact |  | 1,651 |
Distributions |  | (6 | )
​ | ​ | ​ | ​
Balance at December 31, 2017 |  | $ | 12,787 |
​ | ​ | ​ | ​
Retirement Plan Weighted Average Asset Allocations |  |
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
|  | Percentage of plan assets as of December 31, 2017 |
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
|  | US |  | Foreign |
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Equity securities and return seeking assets |  |  | 20% |  |  | —% |
Fixed income, debt securities, or cash |  |  | 80% |  |  | 100% |
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Total |  |  | 100% |  |  | 100% |
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Pension Plans With An Accumulated Benefit Obligation In Excess Of Plan Assets |  |
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
|  | 2017 |  | 2016 |
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
|  | U.S. |  | Foreign |  | U.S. |  | Foreign |
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
|  |  | (Dollars in thousands) |
Accumulated benefit obligation |  | $ | 139,746 |  | $ | 18,843 |  | $ | 140,230 |  | $ | 16,057 |
Fair value of plan assets |  |  | 109,845 |  |  | 13,618 |  |  | 100,905 |  |  | 11,142 |
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Pension Plans With Projected Benefit Obligation In Excess Of Plan Assets |  |
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
|  | 2017 |  | 2016 |
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
|  | U.S. |  | Foreign |  | U.S. |  | Foreign |
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
|  |  | (Dollars in thousands) |
Projected benefit obligation |  | $ | 139,746 |  | $ | 20,407 |  | $ | 140,230 |  | $ | 17,415 |
Fair value of plan assets |  |  | 109,845 |  |  | 13,618 |  |  | 100,905 |  |  | 11,142 |
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Projected Future Pension Plan Cash Flow By Year |  |
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
|  | U.S. |  | Foreign |
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
|  |  | (Dollars in thousands) |
Expected contributions in 2018: |  |  |  |  |  |  |
Expected employer contributions |  | $ | 4,542 |  | $ | 558 |
Expected employee contributions |  |  | — |  |  | — |
Estimated future benefit payments reflecting expected future service for the years ending December 31: |  |  |  |  |  |  |
2018 |  |  | 9,086 |  |  | 864 |
2019 |  |  | 9,053 |  |  | 751 |
2020 |  |  | 9,083 |  |  | 743 |
2021 |  |  | 9,116 |  |  | 778 |
2022 |  |  | 9,103 |  |  | 771 |
2023 - 2027 |  |  | 44,783 |  |  | 6,285 |
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Fair Value Of Assets Of, And The Funded Status Of, Postretirement Plans |  |
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
|  | As of December 31, 2017 |  | As of December 31, 2016 |
Postretirement benefits |  | U.S. |  | Foreign |  | U.S. |  | Foreign |
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
|  | (Dollars in thousands) |
Changes in Benefit Obligation: |  |  |  |  |  |  |  |  |  |  |  |  |
Net benefit obligation at beginning of period |  | $ | 10,175 |  | $ | 10,700 |  | $ | 10,859 |  | $ | 11,296 |
Service cost |  |  | — |  |  | 2 |  |  | — |  |  | 4 |
Interest cost |  |  | 333 |  |  | 653 |  |  | 360 |  |  | 764 |
Foreign currency exchange rates |  |  | — |  |  | 931 |  |  | — |  |  | 709 |
Actuarial loss (gain) |  |  | (1,257 | ) |  | 742 |  |  | (191 | ) |  | (225 | )
Gross benefits paid |  |  | (790 | ) |  | (856 | ) |  | (853 | ) |  | (855 | )
Plan amendment |  |  | — |  |  | — |  |  | — |  |  | (993 | )
Net benefit obligation at end of period |  | $ | 8,461 |  | $ | 12,172 |  | $ | 10,175 |  | $ | 10,700 |
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Changes in Plan Assets: |  |  |  |  |  |  |  |  |  |  |  |  |
Fair value of plan assets at beginning of period |  | $ | — |  | $ | — |  | $ | — |  | $ | — |
Employer contributions |  |  | 790 |  |  | 856 |  |  | 853 |  |  | 855 |
Gross benefits paid |  |  | (790 | ) |  | (856 | ) |  | (853 | ) |  | (855 | )
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Fair value of plan assets at end of period |  | $ | — |  | $ | — |  | $ | — |  | $ | — |
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Funded status: |  | $ | (8,461 | ) | $ | (12,172 | ) | $ | (10,175 | ) | $ | (10,700 | )
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Amounts recognized in accumulated other comprehensive loss: |  |  |  |  |  |  |  |  |  |  |  |  |
Prior service credit |  | $ | — |  | $ | — |  | $ | — |  | $ | — |
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Amounts recognized in the statement of financial position: |  |  |  |  |  |  |  |  |  |  |  |  |
Current liabilities |  | $ | (855 | ) | $ | (912 | ) | $ | (1,134 | ) | $ | (738 | )
Non-current liabilities |  |  | (7,606 | ) |  | (11,260 | ) |  | (9,041 | ) |  | (9,962 | )
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Net amount recognized |  | $ | (8,461 | ) | $ | (12,172 | ) | $ | (10,175 | ) | $ | (10,700 | )
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Assumptions Used To Determine Net Pension Costs And Projected Benefit Obligations |  |
​ | ​ | ​ | ​ | ​ | ​
|  | As of December 31, |
​ | ​ | ​ | ​ | ​ | ​
|  | 2017 |  | 2016 |
​ | ​ | ​ | ​ | ​ | ​
Pension Benefit Obligations Key Assumptions |  |  |  |  |
Weighted average assumptions to determine benefit obligations: |  |  |  |  |
Discount rate |  | 3.20% |  | 3.61% |
Rate of compensation increase |  | 1.57% |  | 1.57% |
Pension Cost Key Assumptions |  |  |  |  |
Weighted average assumptions to determine net cost: |  |  |  |  |
Discount rate |  | 3.61% |  | 3.86% |
Expected return on plan assets |  | 4.95% |  | 4.97% |
Rate of compensation increase |  | 1.57% |  | 1.84% |
​ | ​ | ​ | ​ | ​ | ​
Postretirement benefit obligations
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
|  | 2017 |  | 2016 |
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Weighted average assumptions to determine benefit obligations: |  |  |  |  |  |  |
Discount rate |  |  | 5.07% |  |  | 4.80% |
Health care cost trend on covered charges: |  |  |  |  |  |  |
Initial |  |  | 6.86% |  |  | 6.80% |
Ultimate |  |  | 6.23% |  |  | 5.96% |
Years to ultimate |  |  | 8 |  |  | 8 |
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Postretirement benefit costs
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
|  | 2017 |  | 2016 |
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Weighted average assumptions to determine net cost: |  |  |  |  |  |  |
Discount rate |  |  | 4.80% |  |  | 5.10% |
Health care cost trend on covered charges: |  |  |  |  |  |  |
Initial |  |  | 6.80% |  |  | 6.67% |
Ultimate |  |  | 5.96% |  |  | 6.48% |
Years to ultimate |  |  | 7 |  |  | 1 |
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
One-Percentage Point Change In Assumed Health Care Cost Trend Rates |  | A one-percentage point change in assumed health care cost trend rates would have the following effects at December 31, 2017:
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
|  | One percentage point increase |  | One percentage point decrease |
|  | U.S. |  | Foreign |  | U.S. |  | Foreign |
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
|  | (Dollars in thousands) |
Effect on total service cost and interest cost components |  | $ | 2 |  | $ | 60 |  | $ | (2 | ) | $ | (50 | )
Effect on benefit obligations |  | $ | 28 |  | $ | 639 |  | $ | (27 | ) | $ | (546 | )
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Projected Future Postretirement Cash Flow By Year |  |
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
|  | U.S. |  | Foreign |
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
|  | (Dollars in thousands) |
Expected contributions in 2018: |  |  |  |  |  |  |
Expected employer contributions |  | $ | 855 |  | $ | 912 |
Expected employee contributions |  |  | — |  |  | — |
Estimated future benefit payments reflecting expected future service for the years ending December 31: |  |  |  |  |  |  |
2018 |  |  | 855 |  |  | 912 |
2019 |  |  | 800 |  |  | 907 |
2020 |  |  | 740 |  |  | 909 |
2021 |  |  | 678 |  |  | 900 |
2022 |  |  | 622 |  |  | 885 |
2020 - 2024 |  |  | 2,415 |  |  | 4,518 |
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Pension Costs |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |
Schedule Of Benefit Plans | The components of our consolidated net pension costs are set forth in the following table:
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
|  |  | For the six months ended June 30, |
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
|  | 2018 |  | 2017 |
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
(Dollars in thousands) |
Service cost |  | $ | 996 |  | $ | 992 |
Interest cost |  |  | 2,482 |  |  | 2,769 |
Expected return on plan assets |  |  | (3,004 | ) |  | (2,777 | )
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Net cost |  | $ | 474 |  | $ | 984 |
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
|  | Successor |
|  | 2017 |  | 2016 |  | For the period August 15 through December 31, 2015 |
|  | U.S. |  | Foreign |  | U.S. |  | Foreign |  | U.S. |  | Foreign |
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
|  |  |  |  |  | (Dollars in thousands) |
Service cost |  | $ | 1,305 |  | $ | 710 |  | $ | 1,325 |  | $ | 698 |  | $ | 386 |  | $ | 281 |
Interest cost |  | 5,352 |  | 199 |  | 5,744 |  | 243 |  | 2,200 |  | 94 |
Expected return on assets |  | (5,268 | ) | (299 | ) | (4,940 | ) | (298 | ) | (1,885 | ) | (59 | )
Curtailment gain |  | — |  | — |  | — |  | — |  | — |  | (675 | )
Mark-to-market loss (gain) |  | (4,140 | ) | (53 | ) | (2,322 | ) | (220 | ) | 716 |  | 1,843 |
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Pension costs |  | $ | (2,751 | ) | $ | 557 |  | $ | (193 | ) | $ | 423 |  | $ | 1,417 |  | $ | 1,484 |
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | ​ | ​ | ​ | ​
|  | Predecessor |
|  | For the period January 1 through August 14, 2015 |
|  | U.S. |  | Foreign |
​ | ​ | ​ | ​ | ​ | ​
Service cost |  | $ | 151 |  | $ | 98 |
Interest cost |  | 854 |  | 554 |
Amortization of prior service cost |  | — |  | (12 | )
​ | ​ | ​ | ​ | ​ | ​
Pension costs |  | $ | 1,005 |  | $ | 640 |
​ | ​ | ​ | ​ | ​ | ​
Postretirement Costs |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |
Schedule Of Benefit Plans | The components of our consolidated net postretirement costs are set forth in the following table:
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
For the six months ended June 30, |
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
|  | 2018 |  | 2017 |
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
(Dollars in thousands) |
Service cost |  | $ | — |  | $ | 1 |
Interest cost |  |  | 502 |  |  | 483 |
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Net cost |  | $ | 502 |  | $ | 484 |
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
|  |  | Successor |
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
|  |  |  |  |  |  |  |  |  |  |  |  |  |  | For the period August 15 through |
|  |  | 2017 |  |  | 2016 |  |  | December 31, 2015 |
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
|  | U.S. |  | Foreign |  | U.S. |  | Foreign |  | U.S. |  | Foreign |
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
|  |  | (Dollars in thousands) |
Service cost |  | $ | — |  | $ | 2 |  | $ | — |  | $ | 4 |  |  | — |  | $ | 5 |
Interest cost |  |  | 333 |  |  | 653 |  |  | 360 |  |  | 764 |  |  | 142 |  |  | 289 |
Plan amendment / curtailment |  |  | — |  |  | — |  |  | — |  |  | (993 | ) |  | — |  |  | — |
Mark-to-market (gain) loss |  |  | (1,257 | ) |  | 742 |  |  | (191 | ) |  | (225 | ) |  | (100 | ) |  | (621 | )
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Post-employment benefits cost (benefit) |  | $ | (924 | ) | $ | 1,397 |  | $ | 169 |  | $ | (450 | ) | $ | 42 |  | $ | (327 | )
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | ​ | ​ | ​ | ​
|  | Successor |
​ | ​ | ​ | ​ | ​ | ​
|  | For the period January 1 through August 14, 2015 |
​ | ​ | ​ | ​ | ​ | ​
|  | U.S. |  | Foreign |
​ | ​ | ​ | ​ | ​ | ​
|  | (Dollars in thousands) |
Service cost |  | $ | — |  | $ | 9 |
Interest cost |  | 223 |  | 433 |
Plan amendment / curtailment |  | — |  | — |
Mark-to-market (gain) loss |  | — |  | — |
​ | ​ | ​ | ​ | ​ | ​
Post-employment benefits cost (benefit) |  | $ | 223 |  | $ | 442 |
​ | ​ | ​ | ​ | ​ | ​

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- Definition Fair value of assets of, and the funded status of, postretirement plans [Table Text Block]. + References No definition available. + Details
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- Definition Pension plans' benefit obligations, fair value of assets, and funded status [Table Text Block]. + References No definition available. + Details
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- Definition Retirement plan weighted average asset allocations [Table Text Block]. + References No definition available. + Details
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- Definition Schedule of projected future postretirement cash flow by year [Table Text Block]. + References No definition available. + Details
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- Definition Schedule of projected future retirements cash flow by year [Table Text Block]. + References No definition available. + Details
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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- Definition Tabular disclosure of benefit obligations including accumulated benefit obligation and projected benefit obligation. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
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- Definition Tabular disclosure of accumulated benefit obligations and fair values of plan assets of pension plans and/or other employee benefit plans where the accumulated benefit obligation exceeds the fair value of plan assets. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 3 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e2417-114920 + Details
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- Definition Tabular disclosure of the net gain (loss) and net prior service cost or credit recognized in other comprehensive income (loss) for the period for pension plans and/or other employee benefit plans, and reclassification adjustments of other comprehensive income (loss) for the period, as those amounts, including amortization of the net transition asset or obligation, are recognized as components of net periodic benefit cost. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (i) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
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- Definition Tabular disclosure of the assumptions used to determine for pension plans and/or other employee benefit plans the benefit obligation and net benefit cost, including assumed discount rates, rate increase in compensation increase, and expected long-term rates of return on plan assets. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (k) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
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- Definition Tabular disclosure of the aggregate benefit obligation and aggregate fair value of plan assets for pension plans and/or other employee benefit plans with benefit obligations in excess of plan assets as of the measurement date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 3 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e2417-114920 + Details
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- Definition Tabular disclosure of the reconciliation of beginning and ending balances of the fair value of plan assets of pension plans and/or other employee benefit plans showing separately, if applicable, the effects during the period attributable to each of the following: actual return on plan assets, foreign currency exchange rate changes, contributions by the employer, contributions by plan participants, benefits paid, business combinations, divestitures, and settlements. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
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- Definition Tabular disclosure of one or more of the entity's defined benefit pension plans or one or more other defined benefit postretirement plans, separately for pension plans and other postretirement benefit plans including the entity's schedule of fair value of plan assets for defined benefit or other postretirement plans. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e2439-114920 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e2417-114920 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e2410-114920 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 55 -Paragraph 17 -URI http://asc.fasb.org/extlink&oid=77993564&loc=d3e4179-114921 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
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- Definition Tabular disclosure of the effect of a one-percentage-point increase and the effect of a one-percentage-point decrease in the assumed health care cost trend rates on the aggregate of the service and interest cost components of net periodic postretirement health care benefit costs and the accumulated postretirement benefit obligation for health care benefits. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (m) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
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