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Multiemployer Plans (Details) $ in Thousands | 12 Months Ended
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Dec. 31, 2017 USD ($) item | Dec. 31, 2016 USD ($) item | Dec. 31, 2015 USD ($) item
Multiemployer plans |  |  |
Number of pension plans in which annual contribution was made by the entity during last three years | item | 78 |  |
Number of pension plans in which the entity contributed | item | 0 | 0 | 2
Contributions for significant plans | $ 29,430 | $ 20,544 | $ 21,566
Contributions to other multiemployer plans | 17,505 | 13,639 | 12,730
Total contributions made | 46,935 | 34,183 | 34,296
One Plan |  |  |
Multiemployer plans |  |  |
Contributions for specified plans |  |  | 2,200
Second Plan |  |  |
Multiemployer plans |  |  |
Contributions for specified plans |  |  | 500
Central Pension Fund of the International Union of Operating Engineers and Participating Employers |  |  |
Multiemployer plans |  |  |
Contributions for significant plans | 7,562 | 5,373 | 5,659
Pipeline Industry Benefit Fund |  |  |
Multiemployer plans |  |  |
Contributions for significant plans | 6,050 | 2,740 | 3,783
Laborers International Union of North America National (Industrial) Pension Fund |  |  |
Multiemployer plans |  |  |
Contributions for significant plans | 4,658 | 2,415 | 3,287
Southern California Pipetrades Trust Funds |  |  |
Multiemployer plans |  |  |
Contributions for significant plans | 3,219 | 2,614 | 2,180
Laborers Pension Trust Fund for Northern California |  |  |
Multiemployer plans |  |  |
Contributions for significant plans | 2,945 | 3,598 | 3,150
National Pension Fund |  |  |
Multiemployer plans |  |  |
Contributions for significant plans | 2,548 | 2,161 | 2,106
Operating Engineer Trust Funds |  |  |
Multiemployer plans |  |  |
Contributions for significant plans | $ 2,448 | $ 1,643 | $ 1,401

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- Definition Represents the number of pension plans in which the entity contributed to more than 5% of the plan's total contributions. + References No definition available. + Details
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- Definition Represents the number of pension plans in which annual contribution was made by the entity during the last three years. + References No definition available. + Details
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- Definition Represents the amount of contributions made to the specified multiemployer plan by all employers who participate in the plan. 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 No definition available. + Details
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- Definition Represents the amount of contributions made to the other multiemployer plan by all employers who participate in the plan. 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 No definition available. + Details
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- Definition Represents the amount of contributions made to the significant multiemployer plan by all employers who participate in the plan. 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 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 Amount of contributions made to multiemployer plan by all employers who participate in plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 80 -Section 50 -Paragraph 7 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=65877416&loc=SL14450678-114947 + Details
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