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CONCENTRATION OF CREDIT RISK AND MAJOR CUSTOMERS | 12 Months Ended
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Dec. 31, 2020
CONCENTRATION OF CREDIT RISK AND MAJOR CUSTOMERS |
CONCENTRATION OF CREDIT RISK AND MAJOR CUSTOMERS | 23.CONCENTRATION OF CREDIT RISK AND MAJOR CUSTOMERS ​ The international coal market has been a substantial part of our business with indirect sales to end-users in Europe, Africa, Asia, North America and South America. Our sales into the international coal market are considered exports and are made through brokered transactions. During the years ended December 31, 2020, 2019 and 2018, export tons represented approximately 3.3%, 17.9% and 27.8% of tons sold, respectively. ​ We use the end-usage point as the basis for attributing tons to individual countries. Because title to our export shipments typically transfers to our brokerage customers at a point that does not necessarily reflect the end-usage point, we attribute export tons to the country with the end-usage point, if known. No individual country was attributed greater than 10% of total domestic and export tons sold during the years ended December 31, 2020, 2019 and 2018. ​ We have significant long-term coal supply agreements, some of which contain prospective price adjustment provisions designed to reflect changes in market conditions, labor and other production costs and, in the infrequent circumstance when the coal is sold other than free on board the mine, changes in transportation rates. Our major customers are defined as those customers from which we derive at least ten percent of our total revenues, including transportation revenues. Total revenues from major customers are as follows: ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | ​ | ​ | Year Ended December 31, |
​ |  | Segment |  | 2020 | ​ | 2019 | ​ | 2018 |
​ | ​ | ​ | ​ | (in thousands) | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Customer A |  | Illinois Basin | ​ | $ | 197,379 | ​ | $ | 228,500 | ​ | $ | 219,115 | ​
Customer B | ​ | Appalachia | ​ | ​ | — | ​ | ​ | 213,319 | ​ | ​ | — | ​
Customer C | ​ | Illinois Basin | ​ | ​ | 157,271 | ​ | ​ | — | ​ | ​ | — | ​
Customer D |  | Illinois Basin/Appalachia | ​ |  | 137,785 | ​ | ​ | — | ​ |  | — | ​
​ Trade accounts receivable from major customers totaled approximately $32.0 million and $26.3 million at December 31, 2020 and 2019, respectively. Our bad debt experience has historically been insignificant. Financial conditions of our customers could result in a material change to our bad debt expense in future periods. The coal supply agreements with these customers expire in 2022 for Customer C and Customer D and 2020 for Customer A.

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- Definition The entire disclosure for any concentrations existing at the date of the financial statements that make an entity vulnerable to a reasonably possible, near-term, severe impact. This disclosure informs financial statement users about the general nature of the risk associated with the concentration, and may indicate the percentage of concentration risk as of the balance sheet date. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 275 -URI http://asc.fasb.org/topic&trid=2134479 + Details
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