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Provisions - Employee obligations - North America - Provisions- (Details) $ in Thousands | 12 Months Ended |
--- | --- | ---
Dec. 31, 2018 USD ($) age plan | Dec. 31, 2017 USD ($) age
Post Retirement Plans |  |
Estimated Future Benefit Payments [Abstract] |  |
Percentage of reasonably possible increase in actuarial assumption | 1.00% | 1.00%
Increase (decrease) in defined benefit obligation due to reasonably possible increase in actuarial assumption | $ 1,535 | $ 1,862
Percentage of reasonably possible decrease in actuarial assumption | 1.00% | 1.00%
Increase (decrease) in defined benefit obligation due to reasonably possible decrease in actuarial assumption | $ (1,194) | $ (1,442)
North America |  |
Reconciliation Of Benefit Obligation Plan Assets And Funded Status [Abstract] |  |
Benefit obligation | 64,832 | 71,820
Fair value of plan assets | (46,114) | (52,152)
Provision for pensions | 18,718 | 19,668
Actuarial Assumptions Used To Calculate Defined Benefit Obligation [Abstract] |  |
Discretionary contributions to the defined benefit pension and postretirement plans | 1,037 |
North America | Pension Plans |  |
Reconciliation Of Benefit Obligation Plan Assets And Funded Status [Abstract] |  |
Benefit obligation | 57,455 | 62,983
North America | Post Retirement Plans |  |
Reconciliation Of Benefit Obligation Plan Assets And Funded Status [Abstract] |  |
Benefit obligation | 7,377 | 8,837
USA | Pension Plans |  |
Reconciliation Of Benefit Obligation Plan Assets And Funded Status [Abstract] |  |
Benefit obligation | 35,062 | 38,195
Fair value of plan assets | (29,038) | (32,869)
Provision for pensions | $ 6,024 | $ 5,326
Actuarial Assumptions Used To Calculate Defined Benefit Obligation [Abstract] |  |
Discount rate | 4.00% | 3.50%
Retirement age | age | 65 | 65
CANADA | Pension Plans |  |
Reconciliation Of Benefit Obligation Plan Assets And Funded Status [Abstract] |  |
Benefit obligation | $ 22,393 | $ 24,788
Fair value of plan assets | (17,076) | (19,283)
Provision for pensions | $ 5,317 | $ 5,505
Actuarial Assumptions Used To Calculate Defined Benefit Obligation [Abstract] |  |
Discount rate | 3.80% | 3.60%
Retirement age | age | 62 | 62
CANADA | Post Retirement Plans |  |
Reconciliation Of Benefit Obligation Plan Assets And Funded Status [Abstract] |  |
Benefit obligation | $ 7,377 | $ 8,837
Provision for pensions | $ 7,377 | $ 8,837
Actuarial Assumptions Used To Calculate Defined Benefit Obligation [Abstract] |  |
Discount rate | 3.90% | 3.65%
Retirement age | age | 62 | 62
Minimum | CANADA | Pension Plans |  |
Actuarial Assumptions Used To Calculate Defined Benefit Obligation [Abstract] |  |
Salary increase | 2.75% | 2.75%
Maximum | CANADA | Pension Plans |  |
Actuarial Assumptions Used To Calculate Defined Benefit Obligation [Abstract] |  |
Salary increase | 3.00% | 3.00%
Not later than one year | Actuarial assumption of medical cost trend rates [member] |  |
Estimated Future Benefit Payments [Abstract] |  |
Health care cost trend rate | 5.30% |
Not later than one year | North America | Pension Plans |  |
Estimated Future Benefit Payments [Abstract] |  |
Estimated future benefit payments | $ 3,175 |
Not later than one year | North America | Post Retirement Plans |  |
Estimated Future Benefit Payments [Abstract] |  |
Estimated future benefit payments | 197 |
Later than one year and not later than two years | North America | Pension Plans |  |
Estimated Future Benefit Payments [Abstract] |  |
Estimated future benefit payments | 3,205 |
Later than one year and not later than two years | North America | Post Retirement Plans |  |
Estimated Future Benefit Payments [Abstract] |  |
Estimated future benefit payments | 197 |
Later than two years and not later than three years | North America | Pension Plans |  |
Estimated Future Benefit Payments [Abstract] |  |
Estimated future benefit payments | 3,241 |
Later than two years and not later than three years | North America | Post Retirement Plans |  |
Estimated Future Benefit Payments [Abstract] |  |
Estimated future benefit payments | 203 |
Later than three years and not later than four years | North America | Pension Plans |  |
Estimated Future Benefit Payments [Abstract] |  |
Estimated future benefit payments | 3,247 |
Later than three years and not later than four years | North America | Post Retirement Plans |  |
Estimated Future Benefit Payments [Abstract] |  |
Estimated future benefit payments | 203 |
Later than four years and not later than five years | North America | Pension Plans |  |
Estimated Future Benefit Payments [Abstract] |  |
Estimated future benefit payments | 3,311 |
Later than four years and not later than five years | North America | Post Retirement Plans |  |
Estimated Future Benefit Payments [Abstract] |  |
Estimated future benefit payments | 222 |
Later than five years and not later than ten years [member] | North America | Pension Plans |  |
Estimated Future Benefit Payments [Abstract] |  |
Estimated future benefit payments | 17,178 |
Later than five years and not later than ten years [member] | North America | Post Retirement Plans |  |
Estimated Future Benefit Payments [Abstract] |  |
Estimated future benefit payments | $ 1,393 |
Later Than Sixteen Years And Not Later Than Seventeen Years [Member] | Actuarial assumption of medical cost trend rates [member] |  |
Estimated Future Benefit Payments [Abstract] |  |
Health care cost trend rate | 4.00% |
Globe Metallurgical Inc [Member] | North America | Non Contributory Plans [Member] |  |
Disclosure of defined benefit plans [line items] |  |
Number of defined benefit plans sponsored | plan | 3 |

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