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Employee and Retiree Benefit Plans - Narrative (Details) $ in Thousands | 12 Months Ended | 120 Months Ended
--- | --- | ---
Dec. 31, 2020 USD ($) investment fund | Dec. 31, 2019 USD ($) | Dec. 31, 2018 USD ($) | Dec. 31, 2020 USD ($) fund
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Increase in pension and other postretirement benefit liabilities | $ 63,000 |  |  |
Future annual rate of increase in cost of health care to measure postretirement benefit obligations | 6.20% |  |  | 6.20%
Ultimate rate of health care cost | 4.50% |  |  | 4.50%
Plan asset, maximum investment in any one issuer | 10.00% |  |  | 10.00%
Equity securities minimum market capitalization | $ 100,000 |  |  | $ 100,000
Fixed income portfolio, maximum average maturity years | 11 years |  |  |
Number of funds (in funds) | fund | 2 |  |  | 2
Weighted average expected return on plan asset | 4.70% |  |  |
Basis used to determine expected return on plan asset, average expected investment expenses | 0.60% |  |  |
Perentage return on plan assets over the last ten years |  |  |  | 7.55%
Number of investments in hedge funds and other alternative investments (in investments) | investment | 3 |  |  |
Defined benefit plan, percentage of employer's matching contribution | 6.00% |  |  |
Thrift plan expense | $ 6,600 | $ 8,400 | $ 5,200 |
Equity securities |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Weighted average expected return on plan asset | 3.90% |  |  |
Fixed income securities |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Weighted average expected return on plan asset | 0.80% |  |  |
Equity funds |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Domestic plan, investment notice period | 10 days |  |  |
Pension Benefits |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Contributions to benefit plans | $ 30,178 | $ 25,915 |  |
Weighted average expected return on plan asset | 4.43% | 5.05% |  |
Pension Benefits | U.S. |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Contributions to benefit plans | $ 30,500 |  |  |
Contributions to benefit plans, next fiscal year | 31,300 |  |  | $ 31,300
Pension Benefits | Foreign Plans |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Contributions to benefit plans, next fiscal year | 5,300 |  |  | 5,300
Other Postretirement Benefits |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Contributions to benefit plans | $ 1,770 | $ 2,333 |  |
Weighted average expected return on plan asset | 0.00% | 0.00% |  |
Other Postretirement Benefits | U.S. |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Contributions to benefit plans | $ 1,800 |  |  |
Contributions to benefit plans, next fiscal year | $ 5,300 |  |  | $ 5,300
Second investment |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Domestic plan, investment notice period | 90 days |  |  |
Third investment |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Domestic plan, investment notice period | 95 days |  |  |
Domestic plan, investment lock up period | 2 years |  |  |

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