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Retirement Plans (Details 10) - USD ($) $ in Thousands | 12 Months Ended |  |
--- | --- | --- | ---
Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Fair value of defined benefit plan assets |  | $ 257,488 |  | $ 219,355 |  |
Investments valued at NAV |  | $ 7,935 |  | 7,389 |  |
Redemption terms for investments valued at NAV |  | The redemption terms for the hedge funds are generally quarterly with a 90 day notification period and there are no redemption restrictions. |  |  |  |
Portion in Fair Value Hierarchy [Member] |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Fair value of defined benefit plan assets |  | $ 249,553 |  | 211,966 |  |
Quoted Prices in Active Market for Identical Assets (Level 1) | Portion in Fair Value Hierarchy [Member] |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Fair value of defined benefit plan assets |  | 197,590 |  | 166,145 |  |
Significant Other Observable Inputs (Level 2) | Portion in Fair Value Hierarchy [Member] |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Fair value of defined benefit plan assets |  |  |  | 728 |  |
Significant Unobservable Inputs (Level 3) | Portion in Fair Value Hierarchy [Member] |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Fair value of defined benefit plan assets |  | 51,963 |  | 45,093 |  |
Bank and Insurance Investment Contracts [Member] | Significant Unobservable Inputs (Level 3) |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Fair value of defined benefit plan assets |  | 51,963 |  | 45,093 |  | $ 38,943
U.S. Pension Plans |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Fair value of defined benefit plan assets |  | 171,373 |  | 144,665 |  | 136,128
U.S. Pension Plans | Portion in Fair Value Hierarchy [Member] |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Fair value of defined benefit plan assets |  | 163,438 |  | 137,276 |  |
U.S. Pension Plans | Quoted Prices in Active Market for Identical Assets (Level 1) | Portion in Fair Value Hierarchy [Member] |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Fair value of defined benefit plan assets |  | 163,438 |  | 136,548 |  |
U.S. Pension Plans | Significant Other Observable Inputs (Level 2) | Portion in Fair Value Hierarchy [Member] |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Fair value of defined benefit plan assets |  |  |  | 728 |  |
U.S. Pension Plans | Mutual Funds [Member] | Portion in Fair Value Hierarchy [Member] |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Fair value of defined benefit plan assets |  | $ 163,438 | [1] | $ 136,548 | [2] |
U.S. Pension Plans | Mutual Funds [Member] | Portion in Fair Value Hierarchy [Member] | Large-Cap U S Companies [Member] |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Components of plan asset categories |  | 45.00% |  | 35.00% |  |
U.S. Pension Plans | Mutual Funds [Member] | Portion in Fair Value Hierarchy [Member] | International Growth Companies [Member] |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Components of plan asset categories |  | 30.00% |  | 38.00% |  |
U.S. Pension Plans | Mutual Funds [Member] | Portion in Fair Value Hierarchy [Member] | Fixed Income Bonds [Member] |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Components of plan asset categories |  | 25.00% |  | 27.00% |  |
U.S. Pension Plans | Mutual Funds [Member] | Quoted Prices in Active Market for Identical Assets (Level 1) | Portion in Fair Value Hierarchy [Member] |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Fair value of defined benefit plan assets |  | $ 163,438 | [1] | $ 136,548 | [2] |
U.S. Pension Plans | Cash and Cash Equivalents [Member] | Portion in Fair Value Hierarchy [Member] |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Fair value of defined benefit plan assets | [3] |  |  | 728 |  |
U.S. Pension Plans | Cash and Cash Equivalents [Member] | Significant Other Observable Inputs (Level 2) | Portion in Fair Value Hierarchy [Member] |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Fair value of defined benefit plan assets | [3] |  |  | 728 |  |
U.S. Retiree Healthcare Plan |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Fair value of defined benefit plan assets |  | 11,125 |  | 9,142 |  | 8,001
U.S. Retiree Healthcare Plan | Portion in Fair Value Hierarchy [Member] |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Fair value of defined benefit plan assets |  | 11,125 |  | 9,142 |  |
U.S. Retiree Healthcare Plan | Quoted Prices in Active Market for Identical Assets (Level 1) | Portion in Fair Value Hierarchy [Member] |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Fair value of defined benefit plan assets |  | 11,125 |  | 9,142 |  |
U.S. Retiree Healthcare Plan | Mutual Funds [Member] | Portion in Fair Value Hierarchy [Member] |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Fair value of defined benefit plan assets |  | $ 11,125 | [4] | $ 9,142 | [5] |
U.S. Retiree Healthcare Plan | Mutual Funds [Member] | Portion in Fair Value Hierarchy [Member] | Large-Cap U S Companies [Member] |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Components of plan asset categories |  | 41.00% |  | 38.00% |  |
U.S. Retiree Healthcare Plan | Mutual Funds [Member] | Portion in Fair Value Hierarchy [Member] | International Growth Companies [Member] |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Components of plan asset categories |  | 24.00% |  | 19.00% |  |
U.S. Retiree Healthcare Plan | Mutual Funds [Member] | Portion in Fair Value Hierarchy [Member] | Fixed Income Bonds [Member] |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Components of plan asset categories |  | 35.00% |  | 43.00% |  |
U.S. Retiree Healthcare Plan | Mutual Funds [Member] | Quoted Prices in Active Market for Identical Assets (Level 1) | Portion in Fair Value Hierarchy [Member] |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Fair value of defined benefit plan assets |  | $ 11,125 | [4] | $ 9,142 | [5] |
Non-U.S. Pension Plans |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Fair value of defined benefit plan assets |  | 74,990 |  | 65,548 |  | $ 60,441
Non-U.S. Pension Plans | Portion in Fair Value Hierarchy [Member] |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Fair value of defined benefit plan assets |  | 74,990 |  | 65,548 |  |
Non-U.S. Pension Plans | Quoted Prices in Active Market for Identical Assets (Level 1) | Portion in Fair Value Hierarchy [Member] |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Fair value of defined benefit plan assets |  | 23,027 |  | 20,455 |  |
Non-U.S. Pension Plans | Significant Unobservable Inputs (Level 3) | Portion in Fair Value Hierarchy [Member] |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Fair value of defined benefit plan assets |  | 51,963 |  | 45,093 |  |
Non-U.S. Pension Plans | Mutual Funds [Member] | Portion in Fair Value Hierarchy [Member] |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Fair value of defined benefit plan assets |  | $ 17,244 | [6] | $ 16,737 | [7] |
Non-U.S. Pension Plans | Mutual Funds [Member] | Portion in Fair Value Hierarchy [Member] | International Growth Companies [Member] |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Components of plan asset categories |  | 32.00% |  | 30.00% |  |
Non-U.S. Pension Plans | Mutual Funds [Member] | Portion in Fair Value Hierarchy [Member] | Fixed Income Bonds [Member] |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Components of plan asset categories |  | 58.00% |  | 56.00% |  |
Non-U.S. Pension Plans | Mutual Funds [Member] | Portion in Fair Value Hierarchy [Member] | Mortgages and Real Estate [Member] |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Components of plan asset categories |  | 1.00% |  | 8.00% |  |
Non-U.S. Pension Plans | Mutual Funds [Member] | Portion in Fair Value Hierarchy [Member] | Other Global Investments [Member] |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Components of plan asset categories |  | 9.00% |  | 6.00% |  |
Non-U.S. Pension Plans | Mutual Funds [Member] | Quoted Prices in Active Market for Identical Assets (Level 1) | Portion in Fair Value Hierarchy [Member] |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Fair value of defined benefit plan assets |  | $ 17,244 | [6] | $ 16,737 | [7] |
Non-U.S. Pension Plans | Cash and Cash Equivalents [Member] | Portion in Fair Value Hierarchy [Member] |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Fair value of defined benefit plan assets | [3] | 5,783 |  | 3,718 |  |
Non-U.S. Pension Plans | Cash and Cash Equivalents [Member] | Quoted Prices in Active Market for Identical Assets (Level 1) | Portion in Fair Value Hierarchy [Member] |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Fair value of defined benefit plan assets | [3] | 5,783 |  | 3,718 |  |
Non-U.S. Pension Plans | Bank and Insurance Investment Contracts [Member] | Portion in Fair Value Hierarchy [Member] |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Fair value of defined benefit plan assets | [8] | 51,963 |  | 45,093 |  |
Non-U.S. Pension Plans | Bank and Insurance Investment Contracts [Member] | Significant Unobservable Inputs (Level 3) | Portion in Fair Value Hierarchy [Member] |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Fair value of defined benefit plan assets | [8] | $ 51,963 |  | $ 45,093 |  |
[1] | The mutual fund balance in the U.S. Pension Plans are invested in the following categories: 45% in the common stock of large-cap U.S. companies, 30% in the common stock of international growth companies and 25% in fixed income bonds issued by U.S. companies and by the U.S. government and its agencies.
[2] | The mutual fund balance in the U.S. Pension Plans are invested in the following categories: 35% in the common stock of large-cap U.S. companies, 38% in the common stock of international growth companies and 27% in fixed income bonds issued by U.S. companies and by the U.S. government and its agencies.
[3] | Primarily represents deposit account funds held with various financial institutions.
[4] | The mutual fund balance in the U.S. Retiree Healthcare Plan is invested in the following categories: 41% in the common stock of large-cap U.S. companies, 24% in the common stock of international growth companies and 35% in fixed income bonds of U.S. companies and U.S. government.
[5] | The mutual fund balance in the U.S. Retiree Healthcare Plan is invested in the following categories: 38% in the common stock of large-cap U.S. companies, 19% in the common stock of international growth companies and 43% in fixed income bonds of U.S. companies and U.S. government.
[6] | The mutual fund balance in the Non-U.S. Pension Plans is primarily invested in the following categories: 58% in international bonds, 32% in the common stock of international companies, 1% in mortgages and real estate and 9% in various other global investments.
[7] | The mutual fund balance in the Non-U.S. Pension Plans is invested in the following categories: 56% in international bonds and 30% in the common stock of international companies, 8% in mortgages and real estate and 6% in various other global investments.
[8] | Amount represents bank and insurance guaranteed investment contracts.

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