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Employee Benefits (Narrative) (Details) | 12 Months Ended
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Dec. 31, 2018 USD ($) employee | Dec. 31, 2017 USD ($)
Employer matching contribution, percent of employees' pay | 100.00% |
Maximum annual contribution per employee, percent | 4.00% |
Participants in employee health plan | employee | 2,481 |
Health care cap per person | $ 200,000 |
Insured capped maximum exposure health care | 17,000,000 |
Employee benefit costs | 15,603,000 | $ 16,223,000
Workers' compensation costs | 3,000,000 | 2,500,000
Insured maximum exposure per employee | 1,000,000 |
Aggregate insurance deductible for employees | $ 4,000,000 |
Percentage claims are below average of peers underground coal mining | 23.00% |
Operating Expense [Member] |  |
Employee benefit costs | $ 15,100,000 | $ 15,800,000

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- Definition Amount of labor-related expenses classified as other. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 225 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03.4) -URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688 + Details
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