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Benefit Plans and Collective Bargaining Agreements - Non-Union Employees Narrative (Details) - 401(k) Employee Stock Ownership Plan - USD ($) | 12 Months Ended
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Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Defined Contribution Plan Disclosure [Line Items] |  |  |
Employee maximum contribution percentage | 100.00% |  |
Employee maximum contribution amount | $ 19,000 |  |
Minimum age to qualify under Economic Growth and Tax Relief Reconciliation Act | 50 years |  |
Employee additional contribution eligible under economic growth and tax relief reconciliation act | $ 6,000 |  |
Employee maximum contribution eligible under economic growth and tax relief reconciliation act | $ 25,000 |  |
Employer maximum contribution percentage match | 100.00% |  |
Matching percentage by employer of employees' gross pay | 4.00% |  |
Matching contributions made by employer | $ 800,000 | $ 700,000 | $ 600,000
Employer discretionary contribution | $ 0 | $ 0 | $ 0

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- Definition Amount of cost for defined contribution plan. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -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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