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Benefit Plans - Narrative (Details) - USD ($) | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items] |  |  |
Minimum percentages of gain loss consider for amortization (in hundredths) | 10.00% |  |
Minimum value of outstanding noncallable bonds used in hypothetical cash flow bond matching exercise | $ 50,000,000 |  |
Future earnings period used in determining the expected average rate of earnings | 20 years |  |
Minimum percentage return should exceed growth in consumer price index annually (in hundredths) | 5.75% |  |
Maximum investment in international mutual funds (in hundredths) | 30.00% |  |
Percent of international mutual funds equity allocation in emerging markets (in hundredths) | 3.00% |  |
Percent of international mutual funds equity allocation in companies primarily based in Europe and the Pacific Basin (in hundredths) | 21.00% |  |
Discretionary profit sharing contribution as a percentage of participant's eligible compensation (in hundredths) | 5.00% |  |
Matching contribution rate on employees' before-tax contributions, first contribution level (in hundredths) | 80.00% |  |
Employee contributions subject to employer match, first contribution level | $ 1,000 |  |
Matching contribution rate on employees' before-tax contributions, second contribution level (in hundredths) | 40.00% |  |
Employee contributions subject to employer match, second contribution level | $ 2,000 |  |
Matching contribution rate on employees' before-tax contributions, hired after 01/01/2014 (in hundredths) | 100.00% |  |
Employee contributions subject to employer match for employees hired after 01/01/2014 (in hundredths) | 4.00% |  |
Profit sharing and 401(k) savings plan expenses | $ 6,000,000 | $ 5,900,000 | $ 5,100,000
Pension Plan |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Lump sum pension plan benefit payments | $ 6,300,000 | $ 11,200,000 |
Pension Plan | Equity securities | Maximum |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Target asset allocations (in hundredths) | 40.00% |  |
Other Postretirement Benefit Plan |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Health care trend rate used for current year (in hundredths) | 6.50% |  |
Health Care Cost Trend Rate Assumed for Next Year (in hundredths) | 6.50% | 6.50% |
Rate to Which the Cost Trend Rate is Assumed to Decline (Ultimate Trend Rate) (in hundredths) | 5.00% | 5.00% |
Other Postretirement Benefit Plan | Equity securities | Maximum |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Target asset allocations (in hundredths) | 100.00% |  |

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- Definition The amount of lump sum payments made from fund for which participants are entitled under a pension plan, including pension benefits, death benefits, and benefits due on termination of employment. This amount is included in total benefit payments from fund. + References No definition available. + Details
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- Definition The future earnings period, in years, used in determining the average rate of earnings expected on the classes of funds invested or to be invested to provide for the benefits of the plans. This was then used in selecting the expected long-term rate of return on assets included in the actuarial assumptions used in the valuation of projected benefit obligations, net periodic benefit costs and accumulated postretirement benefit obligation. + References No definition available. + Details
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- Definition The health care cost trend rate used for pre-65 benefits in the current year which is used to measure the expected cost of benefits covered by the plan (gross eligible charges). This is based upon the annual rate of change in the cost of health care benefits currently provided by the postretirement benefit plan, due to factors other than changes in the composition of the plan population by age and dependency status. + References No definition available. + Details
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- Definition The maximum investment in international mutual funds, as a percentage of the equity investments range, to total plan assets as of the measurement date of the latest statement of financial position. + References No definition available. + Details
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- Definition The minimum value of outstanding noncallable bonds used in a hypothetical cash flow bond matching exercise for purposes of selecting a discount rate related to actuarial assumptions used in the valuation of projected benefit obligations, net periodic benefit costs and accumulated postretirement benefit obligation. + References No definition available. + Details
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- Definition The company's discretionary profit sharing contribution as a percentage of each participant's eligible compensation. + References No definition available. + Details
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- Definition The amount of a participant's before-tax contribution to the 401(k) savings plan subject to company match at the first contribution level. + References No definition available. + Details
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- Definition The amount of a participant's before-tax contribution to the 401(k) savings plan subject to company match for those employees hired after 01/01/2014. + References No definition available. + Details
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- Definition The amount of a participant's before-tax contribution to the 401(k) savings plan subject to company match at the second contribution level. The second contribution level is in addition to the first contribution level. + References No definition available. + Details
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- Definition The percentage at which the company will provide a matching 401(k) savings contribution on employees' before-tax contributions at the first contribution level. + References No definition available. + Details
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- Definition The percentage at which the company will provide a matching 401(k) savings contribution on employees' before-tax contributions for those employees hired after 01/01/2014. + References No definition available. + Details
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- Definition The percentage at which the company will provide a matching 401(k) savings contribution on employees' before-tax contributions at the second contribution level. The second contribution level is in addition to the first contribution level. + References No definition available. + Details
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- Definition The minimum percentages that return should exceed growth in consumer price index annually. + References No definition available. + Details
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- Definition Represents minimum percentages of gain loss consider for amortization. + References No definition available. + Details
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- Definition The investment in international mutual funds primarily based in Europe and the Pacific Basin, as a percentage of the equity investments range. + References No definition available. + Details
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- Definition The investment in international mutual funds (emerging markets), as a percentage of the equity investments range. + References No definition available. + Details
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + 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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- Definition Percentage of target investment allocation to total plan assets. Includes, but is not limited to, percentage on weighted-average basis if more than one 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 (d)(5)(i) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
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- Definition Ultimate trend rate for health care cost for defined benefit postretirement 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 (l) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
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- Definition Amount of cost for defined contribution plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 70 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=49170846&loc=d3e28014-114942 + Details
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