Significant Accounting Policies (Policies) | 3 Months Ended |
Mar. 31, 2019 |
Accounting Policies [Abstract] | |
Basis of Accounting, Policy [Policy Text Block] | Basis of Presentation not 10 December 31, 2018. In the opinion of management, the accompanying unaudited condensed consolidated financial statements include all adjustments, consisting of normal recurring adjustments, necessary to fairly present the financial position as of, and the results of operations for, all periods presented. In preparing the accompanying financial statements, management has made certain estimates and assumptions that affect reported amounts in the condensed consolidated financial statements and disclosures of contingencies. Actual results may not |
Revenue [Policy Text Block] | Revenue Recognition one May 2014, 2014 09, Revenue from Contracts with Customers 2014 09 2014 09, Revenue from Contracts with Customers, January 1, 2018 no For periods subsequent to January 1, 2018, Our coal sales generally include up to 90 not 30 |
Earnings Per Share, Policy [Policy Text Block] | Earnings per Share |
Investment, Policy [Policy Text Block] | Financial Instruments We invested excess cash amounts before its planned expenditure for capital projects in highly-rated securities with the primary objective of achieving competitive low risk interest rate return, while minimizing the potential risk of principal loss. Fair values were determined for each individual security based on observable inputs other than quoted prices in active markets for identical assets and liabilities, quoted prices for identical or similar assets or liabilities in inactive markets, or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the securities. The difference between the carrying amount and fair value of these securities was not Nonrecurring fair value measurements include asset retirement obligations, the estimated fair value of which is calculated as the present value of estimated cash flows related to its reclamation liabilities using Level 3 |
Concentration Risk, Credit Risk, Policy [Policy Text Block] | Concentrations— three March 31, 2019, three 55% three March 31, 2019 28% three March 31, 2018 three 47% |
New Accounting Pronouncements, Policy [Policy Text Block] | Recent Accounting Pronouncements February 2016, 2016 02, Leases 2016 02, Leases, January 1, 2019. not not $0.3 March 31, 2019, not |