XML 58 R37.htm IDEA: XBRL DOCUMENT
v3.3.1.900

Pension and other postretirement benefits (Tables) | 12 Months Ended
--- | ---
Dec. 31, 2015
Compensation and Retirement Disclosure [Abstract] |
Schedule of Changes in Projected Benefit Obligations | The change in benefit obligations and change in plan assets as of December 31 are as follows:
| Pension |  | OPEB
| 2015 | 2014 |  | 2015 | 2014
Change in benefit obligation: |  |  |  |  |
Benefit obligation at beginning of year | $ | 336,292 |  | $ | 238,319 |  |  | $ | 158,781 |  | $ | 134,652 |
Service cost | 6,346 |  | 5,605 |  |  | 1,970 |  | 1,591 |
Interest cost | 13,388 |  | 11,629 |  |  | 5,985 |  | 6,420 |
Plan amendments | — |  | (5,308 | ) |  | (1,758 | ) | — |
Medicare Part D | — |  | — |  |  | — |  | 273 |
Actuarial loss (gain) | (11,429 | ) | 32,772 |  |  | (18,150 | ) | 17,669 |
Acquisition | — |  | 84,743 |  |  | — |  | 2,857 |
Benefits paid | (19,247 | ) | (11,895 | ) |  | (5,878 | ) | (4,681 | )
Curtailment | 1,221 |  | — |  |  | (8,400 | ) | — |
Settlements | — |  | (19,573 | ) |  | — |  | — |
Benefit obligation at end of year | $ | 326,571 |  | $ | 336,292 |  |  | $ | 132,550 |  | $ | 158,781 |
Schedule of Changes in Fair Value of Plan Assets |
| Pension |  | OPEB
| 2015 | 2014 |  | 2015 | 2014
Change in plan assets: |  |  |  |  |
Fair value of plan assets at beginning of year | $ | 305,520 |  | $ | 199,304 |  |  | $ | — |  | $ | — |
Actual return on plan assets | (11,321 | ) | 16,118 |  |  | — |  | — |
Acquisition | — |  | 115,982 |  |  | — |  | — |
Employer contributions | 5,910 |  | 5,584 |  |  | 5,878 |  | 4,681 |
Benefits paid | (19,247 | ) | (11,895 | ) |  | (5,878 | ) | (4,681 | )
Settlements | — |  | (19,573 | ) |  | — |  | — |
Fair value of assets at end of year | $ | 280,862 |  | $ | 305,520 |  |  | $ | — |  | $ | — |
Schedule of Amounts Recognized in Balance Sheet |
| Pension |  | OPEB
| 2015 | 2014 |  | 2015 | 2014
Funded status of plans: |  |  |  |  |
Funded status | $ | (45,709 | ) | $ | (30,772 | ) |  | $ | (132,550 | ) | $ | (158,781 | )
Amounts recognized in the Consolidated Balance Sheets: |  |  |  |  |  |  |  |  |
Non-current assets | $ | — |  | $ | 30,842 |  |  | $ | — |  | $ | — |
Current liabilities | (1,743 | ) | (1,744 | ) |  | (6,551 | ) | (6,118 | )
Non-current liabilities | (43,966 | ) | (59,870 | ) |  | (125,999 | ) | (152,663 | )
Net amount recognized | $ | (45,709 | ) | $ | (30,772 | ) |  | $ | (132,550 | ) | $ | (158,781 | )
Amounts recognized in accumulated other comprehensive loss (pre-tax): |  |  |  |  |  |  |
Net loss | $ | 80,514 |  | $ | 63,360 |  |  | $ | 49,562 |  | $ | 79,720 |
Prior service cost (benefit) | 1,211 |  | 1,335 |  |  | (9,377 | ) | (15,751 | )
Total | $ | 81,725 |  | $ | 64,695 |  |  | $ | 40,185 |  | $ | 63,969 |
Schedule of Net Benefit Cost | Net Periodic Benefit Cost:
| Year Ended December 31,
| Pension |  | OPEB
| 2015 | 2014 | 2013 |  | 2015 | 2014 | 2013
Service cost | $ | 6,346 |  | $ | 5,605 |  | $ | 4,735 |  |  | $ | 1,970 |  | $ | 1,591 |  | $ | 2,527 |
Interest cost | 13,388 |  | 11,629 |  | 8,908 |  |  | 5,985 |  | 6,420 |  | 5,681 |
Expected return on plan assets | (21,241 | ) | (14,694 | ) | (10,592 | ) |  | — |  | — |  | — |
Amortization of prior service costs | 110 |  | 77 |  | 113 |  |  | (3,728 | ) | (3,844 | ) | (3,995 | )
Amortization of net loss | 3,980 |  | 1,907 |  | 3,152 |  |  | 3,814 |  | 3,704 |  | 5,022 |
Settlements | — |  | 4,701 |  | — |  |  | — |  | — |  | — |
Curtailment cost (benefit) | 1,235 |  | 263 |  | (18 | ) |  | (4,266 | ) | — |  | (20 | )
Net periodic benefit cost | $ | 3,818 |  | $ | 9,488 |  | $ | 6,298 |  |  | $ | 3,775 |  | $ | 7,871 |  | $ | 9,215 |
Schedule of Amounts Recognized in Other Comprehensive Income (Loss) | Other changes in Plan Assets and Benefit Obligations Recognized in Other Comprehensive Loss (pre-tax):
| Year Ended December 31,
| Pension |  | OPEB
| 2015 | 2014 |  | 2015 | 2014
Net loss (gain) | $ | 21,133 |  | $ | 24,326 |  |  | $ | (26,686 | ) | $ | 17,669 |
Prior service cost (benefit) | — |  | 1,299 |  |  | (1,758 | ) | — |
Amortization of net loss, including recognition due to settlement | (3,980 | ) | (6,608 | ) |  | (3,814 | ) | (3,704 | )
Amortization of prior service benefit (cost), including recognition due to curtailment | (124 | ) | (340 | ) |  | 8,475 |  | 3,844 |
Total amount recognized in other comprehensive loss | 17,029 |  | 18,677 |  |  | (23,783 | ) | 17,809 |
Net periodic benefit cost | 3,818 |  | 9,488 |  |  | 3,775 |  | 7,871 |
Total recognized in net periodic benefit cost and other comprehensive loss | $ | 20,847 |  | $ | 28,165 |  |  | $ | (20,008 | ) | $ | 25,680 |
Schedule of Amounts in Accumulated Other Comprehensive Income (Loss) to be Recognized over Next Fiscal Year |
Amounts in accumulated other comprehensive loss expected to be recognized as components of net periodic benefit cost during 2016:
| Pension |  | OPEB
Amortization of net loss | $ | 4,161 |  |  | $ | 3,518 |
Amortization of prior service cost (benefit) | 106 |  |  | (2,781 | )
Weighted Average Assumptions Used in Calculating Benefit Obligation and Net Periodic Benefit Cost | Weighted average assumptions used to determine benefit obligations at December 31:
| Pension |  | OPEB
| 2015 | 2014 |  | 2015 | 2014
Discount rate (1) | 4.44% | 4.05% |  | 4.50% | 4.00%
Rate of compensation increase (2) | 3%/4% | 3%/4% |  | 3%/4% | 3%/4%
Measurement date | 12/31/2015 | 12/31/2014 |  | 12/31/2015 | 12/31/2014
Weighted average assumptions used to determine net periodic benefit cost for the years ended December 31:
| Pension |  | OPEB
| 2015 | 2014 | 2013 |  | 2015 | 2014 | 2013
Measurement date | 12/31/2014 | 12/31/2013 | 12/31/2012 |  | 12/31/2014 | 12/31/2013 | 12/31/2012
Fiscal year end | 12/31/2015 | 12/31/2014 | 12/31/2013 |  | 12/31/2015 | 12/31/2014 | 12/31/2013
Discount rate (1) | 4.05% | 4.89% | 4.00% |  | 4.00% | 4.99% | 4.01%
Rate of compensation increase (2) | 3%/4% | 3%/4% | 3%/4% |  | 3%/4% | 3%/4% | 3%/4%
Expected return on plan assets (3) | 7.16% | 7.25% | 7.25% |  | — | — | —
(1) | We use the Ryan Discount Rate Curve ("Ryan Curve") to determine the discount rate.
(2) | For 2015, the rate of compensation increase is 3% per year for the first three years and 4% per year for year four and thereafter. For 2014, the rate of compensation increase is 3% per year for the first four years and 4% per year for year five and thereafter.
For 2013, the rate of compensation increase is 3% per year for the first five years and 4% per year for year six and thereafter.
(3) | The rate for each of our defined benefit plans was selected by taking into account our expected asset mix and is based on historical performance as well as expected future rates of return on plan assets.
Schedule of Effect of One-Percentage-Point Change in Assumed Health Care Cost Trend Rates | A one-percentage-point change in the assumed health care cost trend rate would have had the following effects in 2015:
| 1% Increase |  | 1% Decrease
Effect on total of service and interest cost | $ | 1,403 |  |  | $ | (1,108 | )
Effect on accumulated postretirement benefit obligation | 18,170 |  |  | (15,086 | )
Schedule of Allocation of Plan Assets | The Pension Plans’ weighted average long-term strategic asset allocation policy targets are as follows:
| Pension Plan Asset Allocation
| 2015 Target | December 31, 2015 | December 31, 2014
Equities: |  |  |
U.S. equities | 31% | 30% | 42%
International equities | 21% | 20% | 18%
Fixed income | 48% | 50% | 40%
|  | 100% | 100%
Fair Value of Pension Plans’ assets included under the fair value hierarchy:
As of December 31, 2015 | Level 1 | Level 2 | Level 3 | Total
Equities: |  |  |  |
U.S. equities | $ | 86,723 |  | $ | — |  | $ | — |  | $ | 86,723 |
International equities | 54,769 |  | — |  | — |  | 54,769 |
Fixed income | 139,370 |  | — |  | — |  | 139,370 |
Total | $ | 280,862 |  | $ | — |  | $ | — |  | $ | 280,862 |
As of December 31, 2014 |  |  |  |  |  |  |  |
Equities: |  |  |  |  |  |  |  |
U.S. equities | $ | 79,148 |  | $ | — |  | $ | — |  | $ | 79,148 |
International equities | 33,720 |  | — |  | — |  | 33,720 |
Fixed income | 76,204 |  | — |  | — |  | 76,204 |
Plan Receivable (1) | — |  | — |  | 116,448 |  | 116,448 |
Total | $ | 189,072 |  | $ | — |  | $ | 116,448 |  | $ | 305,520 |
(1) | Represents the receivable to the Century Aluminum of South Carolina defined benefit plan related to pension funding obligations under the Stock Purchase Agreement which was received in 2015. The plan receivable was considered a Level 3 asset because determining the fair value requires significant unobservable inputs, including census data and various actuarial assumptions.
Schedule Of Expected Benefit Plan Contributions | We expect to make the following contributions for 2016:
| 2016
Expected pension plan contributions | $ | 1,769 |
Expected OPEB benefits payments | 6,551 |
Schedule of Expected Benefit Payments | The following table provides the estimated future benefit payments for the pension and other postretirement benefit plans:
| Pension Benefits |  | OPEB Benefits
2016 | $ | 26,438 |  |  | $ | 6,551 |
2017 | 19,755 |  |  | 6,789 |
2018 | 20,228 |  |  | 7,099 |
2019 | 21,229 |  |  | 7,388 |
2020 | 21,655 |  |  | 7,508 |
2021 – 2025 | 105,301 |  |  | 39,031 |
Schedule of Multiemployer Plans | Century’s participation in the plan for the year ended December 31, 2015, is outlined in the table below.
Fund | Steelworkers Pension Trust
EIN / PN | 23-6648508/499
Pension Protection Act Zone Status 2015 (1) | Green
Pension Protection Act Zone Status 2014 (1) | Green
Subject to Financial Improvement/Rehabilitation Plan | No
Contributions of Century Aluminum 2015 | $1,618
Contributions of Century Aluminum 2014 | $2,164
Contributions of Century Aluminum 2013 | $2,171
Withdrawal from Plan Probable | No
Surcharge Imposed | No
Expiration Date of Collective Bargaining Agreement | April 1, 2020
(1) | The most recent Pension Protection Act zone status available in 2015 and 2014 is for the plan's year-end December 31, 2014 and December 31, 2013, respectively. The zone status is based on information that Century received from the plan as well as publicly available information per the Department of Labor and is certified by the plan’s actuary. Among other factors, plans in the green zone are at least 80 percent funded.

X
- Definition Tabular disclosure of contributions expected to be made to defined benefits plans in the next fiscal year. + References No definition available. + Details
Name: | cenx_ScheduleofExpectedBenefitPlanContributionsTableTextBlock
Namespace Prefix: | cenx_
Data Type: | nonnum:textBlockItemType
Balance Type: | na
Period Type: | duration

X
- References No definition available. + Details
Name: | us-gaap_CompensationAndRetirementDisclosureAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Tabular disclosure of the major categories of plan assets of pension plans and/or other employee benefit plans. This information may include, but is not limited to, the target allocation of plan assets, the fair value of each major category of plan assets, and the level within the fair value hierarchy in which the fair value measurements fall. + 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 (d)(5) -URI http://asc.fasb.org/extlink&oid=58740216&loc=d3e1928-114920 + Details
Name: | us-gaap_ScheduleOfAllocationOfPlanAssetsTableTextBlock
Namespace Prefix: | us-gaap_
Data Type: | nonnum:textBlockItemType
Balance Type: | na
Period Type: | duration

X
- Definition Tabular disclosure of the amounts related to pension plans and/or other employee benefit plans in accumulated other comprehensive income (loss) expected to be recognized as components of net periodic benefit cost over the next fiscal year, including the net gain (loss), net prior service cost or credit, and net transition asset or 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 (s) -URI http://asc.fasb.org/extlink&oid=58740216&loc=d3e1928-114920 + Details
Name: | us-gaap_ScheduleOfAmountsInAccumulatedOtherComprehensiveIncomeLossToBeRecognizedOverNextFiscalYearTableTextBlock
Namespace Prefix: | us-gaap_
Data Type: | nonnum:textBlockItemType
Balance Type: | na
Period Type: | duration

X
- Definition Tabular disclosure of the amounts that are recognized in the balance sheet (or statement of financial position) for pension plans and/or other employee benefit plans, showing separately the assets and current and noncurrent liabilities (if applicable) recognized. + 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 (c) -URI http://asc.fasb.org/extlink&oid=58740216&loc=d3e1928-114920 + Details
Name: | us-gaap_ScheduleOfAmountsRecognizedInBalanceSheetTableTextBlock
Namespace Prefix: | us-gaap_
Data Type: | nonnum:textBlockItemType
Balance Type: | na
Period Type: | duration

X
- 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=58740216&loc=d3e1928-114920 + Details
Name: | us-gaap_ScheduleOfAmountsRecognizedInOtherComprehensiveIncomeLossTableTextBlock
Namespace Prefix: | us-gaap_
Data Type: | nonnum:textBlockItemType
Balance Type: | na
Period Type: | duration

X
- 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=58740216&loc=d3e1928-114920 + Details
Name: | us-gaap_ScheduleOfAssumptionsUsedTableTextBlock
Namespace Prefix: | us-gaap_
Data Type: | nonnum:textBlockItemType
Balance Type: | na
Period Type: | duration

X
- 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=58740216&loc=d3e1928-114920 + Details
Name: | us-gaap_ScheduleOfChangesInFairValueOfPlanAssetsTableTextBlock
Namespace Prefix: | us-gaap_
Data Type: | nonnum:textBlockItemType
Balance Type: | na
Period Type: | duration

X
- Definition Tabular disclosure of the change in the benefit obligation of pension plans and/or other employee benefit plans from the beginning to the end of the period, showing separately, if applicable, the effects of the following: service cost, interest cost, contributions by plan participants, actuarial gains and losses, foreign currency exchange rate changes, benefits paid, plan amendments, business combinations, divestitures, curtailments, settlements, and special and contractual termination 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 (a) -URI http://asc.fasb.org/extlink&oid=58740216&loc=d3e1928-114920 + Details
Name: | us-gaap_ScheduleOfChangesInProjectedBenefitObligationsTableTextBlock
Namespace Prefix: | us-gaap_
Data Type: | nonnum:textBlockItemType
Balance Type: | na
Period Type: | duration

X
- 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=58740216&loc=d3e1928-114920 + Details
Name: | us-gaap_ScheduleOfEffectOfOnePercentagePointChangeInAssumedHealthCareCostTrendRatesTableTextBlock
Namespace Prefix: | us-gaap_
Data Type: | nonnum:textBlockItemType
Balance Type: | na
Period Type: | duration

X
- Definition Tabular disclosure of benefits expected to be paid by pension plans and/or other employee benefit plans in each of the next five fiscal years and in the aggregate for the five fiscal years thereafter. + 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 (f) -URI http://asc.fasb.org/extlink&oid=58740216&loc=d3e1928-114920 + Details
Name: | us-gaap_ScheduleOfExpectedBenefitPaymentsTableTextBlock
Namespace Prefix: | us-gaap_
Data Type: | nonnum:textBlockItemType
Balance Type: | na
Period Type: | duration

X
- Definition Tabular disclosure of the quantitative and qualitative information related to multiemployer plans in which the employer participates. A multiemployer plan is a pension or postretirement benefit plan to which two or more unrelated employers contribute where assets contributed by one participating employer may be used to provide benefits to employees of other participating employers. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 80 -Section 50 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=49170332&loc=SL14450657-114947 + Details
Name: | us-gaap_ScheduleOfMultiemployerPlansTableTextBlock
Namespace Prefix: | us-gaap_
Data Type: | nonnum:textBlockItemType
Balance Type: | na
Period Type: | duration

X
- Definition Tabular disclosure of the components of net benefit costs for pension plans and/or other employee benefit plans including service cost, interest cost, expected return on plan assets, gain (loss), prior service cost or credit, transition asset or obligation, and gain (loss) recognized due to settlements or curtailments. + 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 (h) -URI http://asc.fasb.org/extlink&oid=58740216&loc=d3e1928-114920 + Details
Name: | us-gaap_ScheduleOfNetBenefitCostsTableTextBlock
Namespace Prefix: | us-gaap_
Data Type: | nonnum:textBlockItemType
Balance Type: | na
Period Type: | duration