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Post Retirement Benefits - Multiemployer Plans (Details) | 12 Months Ended
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Aug. 10, 2019 $ / h | Aug. 05, 2018 $ / h | Dec. 31, 2017 USD ($) | Aug. 06, 2017 $ / h | Dec. 31, 2016 USD ($) | Dec. 31, 2015 USD ($)
Multiemployer plans: |  |  |  |  |  |  |
Certified zone status, percent funded limit for red status |  |  |  | 65.00% |  |  |
Certified zone status, percent funded limit for yellow status |  |  |  | 80.00% |  |  |
Certified zone status, percent funded limit for green status |  |  |  | 80.00% |  |  |
Multi-employer plan contributions | $ | [1] |  |  | $ 647,000 |  | $ 710,000 | $ 863,000
Multiemployer plan, postretirement benefit |  |  |  |  |  |  |
Multiemployer plans: |  |  |  |  |  |  |
Maximum percentage of total contribution |  |  |  | 5.00% |  |  |
Multiemployer plans, collective-bargaining arrangement, maximum hours of work per week for employer contribution |  |  |  | 40 hours |  |  |
Multiemployer plans, collective-bargaining arrangement, rate of employer contribution |  |  |  |  | 1.45 |  |
Forecast | Multiemployer plan, postretirement benefit |  |  |  |  |  |  |
Multiemployer plans: |  |  |  |  |  |  |
Multiemployer plans, collective-bargaining arrangement, rate of employer contribution |  | 1.55 | 1.50 |  |  |  |
[1] | The plan re-certified its zone status after using the amortization provisions of the Code. The Company's contributions to the plan did not represent more than 5% of total contributions to the plan as indicated in the plan's most recently available annual report for the plan year ended December 31, 2016. Under the terms of the collective-bargaining agreement, the Company is required to make contributions to the plan for each hour worked up to a maximum of 40 hours per person, per week, at the following rates: $1.45 per hour from August 8, 2016 through August 6, 2017; $1.50 per hour from August 7, 2017 through August 5, 2018; $1.55 per hour from August 6, 2018 through August 10, 2019.

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- Definition Multiemployer Plans, Certified Zone Status, Percent Funded Limit for Red Status + References No definition available. + Details
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- Definition Multiemployer Plans, Certified Zone Status, Percent Funded Limit for Yellow Status + References No definition available. + Details
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- Definition Multiemployer Plans, Collective-Bargaining Arrangement, Maximum Hours of Work Per Week for Employer Contribution + References No definition available. + Details
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- Definition Amount of contributions made to multiemployer plan by employer. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 80 -Section 50 -Paragraph 11 -URI http://asc.fasb.org/extlink&oid=65877416&loc=SL14450702-114947 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 80 -Section 50 -Paragraph 5 -Subparagraph (e)(1) -URI http://asc.fasb.org/extlink&oid=65877416&loc=SL14450657-114947 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 80 -Section 50 -Paragraph 9 -URI http://asc.fasb.org/extlink&oid=65877416&loc=SL14450691-114947 + Details
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