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Employee and Retiree Benefit Plans (Narrative) (Details) - USD ($) $ in Thousands | 12 Months Ended | 120 Months Ended
--- | --- | ---
Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015 | Dec. 31, 2017
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Future annual rate of increase in cost of health care for 2016 to measure postretirement benefit obligations | 6.70% |  |  | 6.70%
Ultimate rate of health care cost in 2028 and thereafter | 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 |  |  |
Weighted average expected return on plan asset | 5.64% |  |  |
Basis used to determine expected return on plan asset, average expected investment expenses | 0.60% |  |  |
Perentage return on plan assets |  |  |  | 6.66%
Defined benefit plan, percentage of employer's matching contribution | 6.00% |  |  |
Thrift plan expense | $ 7,800 | $ 7,400 | $ 7,600 |
Investment 2 [Member] |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Domestic plan, investment notice period | 90 days |  |  |
Investment 3 [Member] |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Domestic plan, investment lock up period | 2 years |  |  |
Domestic plan, investment notice period | 95 days |  |  |
Defined Benefit Plan, Equity Securities [Member] |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Weighted average expected return on plan asset | 7.15% |  |  |
Defined Benefit Plan, Equity Securities [Member] | Minimum [Member] |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Target allocations of plan assets | 40.00% |  |  | 40.00%
Defined Benefit Plan, Equity Securities [Member] | Maximum [Member] |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Target allocations of plan assets | 70.00% |  |  | 70.00%
Defined Benefit Plan, Fixed Income Securities [Member] |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Weighted average expected return on plan asset | 4.26% |  |  |
Defined Benefit Plan, Fixed Income Securities [Member] | Minimum [Member] |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Target allocations of plan assets | 30.00% |  |  | 30.00%
Defined Benefit Plan, Fixed Income Securities [Member] | Maximum [Member] |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Target allocations of plan assets | 60.00% |  |  | 60.00%
Defined Benefit Plan, Long/Short Equity [Member] | Minimum [Member] |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Target allocations of plan assets | 0.00% |  |  | 0.00%
Defined Benefit Plan, Long/Short Equity [Member] | Maximum [Member] |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Target allocations of plan assets | 15.00% |  |  | 15.00%
Defined Benefit Plan, Cash And Equivalents [Member] | Minimum [Member] |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Target allocations of plan assets | 0.00% |  |  | 0.00%
Defined Benefit Plan, Cash And Equivalents [Member] | Maximum [Member] |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Target allocations of plan assets | 15.00% |  |  | 15.00%
Defined Benefit Plan, Equity Securities, Emerging Market Commingled Equity Fund [Member] |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Domestic plan, investment notice period | 10 days |  |  |
Canada [Member] | Defined Benefit Plan, Equity Securities [Member] |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Target allocations of plan assets | 60.00% |  |  | 60.00%
Canada [Member] | Defined Benefit Plan, Equity Securities [Member] | Minimum [Member] |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Target allocations of plan assets | 55.00% |  |  | 55.00%
Canada [Member] | Defined Benefit Plan, Equity Securities [Member] | Maximum [Member] |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Target allocations of plan assets | 65.00% |  |  | 65.00%
Canada [Member] | Defined Benefit Plan, Fixed Income Securities [Member] |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Target allocations of plan assets | 35.00% |  |  | 35.00%
Canada [Member] | Defined Benefit Plan, Fixed Income Securities [Member] | Minimum [Member] |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Target allocations of plan assets | 30.00% |  |  | 30.00%
Canada [Member] | Defined Benefit Plan, Fixed Income Securities [Member] | Maximum [Member] |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Target allocations of plan assets | 40.00% |  |  | 40.00%
Canada [Member] | Defined Benefit Plan, Cash [Member] |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Target allocations of plan assets | 5.00% |  |  | 5.00%
Canada [Member] | Defined Benefit Plan, Cash [Member] | Minimum [Member] |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Target allocations of plan assets | 0.00% |  |  | 0.00%
Canada [Member] | Defined Benefit Plan, Cash [Member] | Maximum [Member] |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Target allocations of plan assets | 10.00% |  |  | 10.00%
United Kingdom [Member] |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Target interest and inflation rate hedge ratio | 100.00% |  |  |
United Kingdom [Member] | Defined Benefit Plan, Equity Securities [Member] |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Target allocations of plan assets | 60.00% |  |  | 60.00%
United Kingdom [Member] | Defined Benefit Plan, Fixed Income Securities [Member] |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Target allocations of plan assets | 40.00% |  |  | 40.00%
Pension Benefits [Member] |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Contributions to benefit plans | $ 24,918 | $ 8,186 |  |
Weighted average expected return on plan asset | 5.64% | 5.62% |  |
Pension Benefits [Member] | United States [Member] |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Contributions to benefit plans | $ 18,000 |  |  |
Expected benefit plan contributions to be made during next year | 24,400 |  |  | $ 24,400
Pension Benefits [Member] | Foreign Plans [Member] |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Contributions to benefit plans | 6,900 |  |  |
Expected benefit plan contributions to be made during next year | 600 |  |  | 600
Other Postretirement Benefits [Member] |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Contributions to benefit plans | 2,417 | $ 3,581 |  |
Other Postretirement Benefits [Member] | United States [Member] |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Contributions to benefit plans | 2,400 |  |  |
Expected benefit plan contributions to be made during next year | $ 5,400 |  |  | $ 5,400

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- Definition Weighted average rate of return on plan assets, reflecting average rate of earnings expected on existing plan assets and expected contributions, used to determine net periodic benefit cost of defined benefit plan. + 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)(3) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
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- Definition Amount of contribution received by defined benefit plan from employer which increases 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 (d)(5)(ii) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 6 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e2709-114920 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (b)(3) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(5)(iv)(01) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
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- Definition Assumed rate, for next fiscal year, based on annual change in cost of health care cost benefits used to measure expected cost of benefits covered by defined benefit postretirement plan. Factors include, but are not limited to, estimate of health care inflation, change in health care utilization or delivery pattern, technological advances, and change in health status of participant. Excludes factors for change in composition of plan population by age and dependency status. + 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 (l) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
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