Revenue	3 Months Ended
Mar. 31, 2019
Revenue from Contract with Customer [Abstract]
Revenue	(12)REVENUE Effective January 1, 2018, we adopted ASU 2014-09. The adoption of this standard did not impact the timing of revenue recognition on our consolidated balance sheets or condensed consolidated statements of comprehensive income. Revenue from Contracts with Customers We account for a contract with a customer when the parties have approved the contract and are committed to performing their respective obligations, the rights of each party are identified, payment terms are identified, the contract has commercial substance, and collectability of consideration is probable. We recognize revenue when we satisfy a performance obligation by transferring control of a good or service to a customer. Our revenue is derived from sales to customers of coal produced at our facilities. Our customers purchase coal directly from our mine sites and our Princeton Loop, where the sale occurs and where title, risk of loss, and control typically pass to the customer at that point. Our customers arrange for and bear the costs of transporting their coal from our mines to their plants or other specified discharge points. Our customers are typically domestic utility companies. Our coal sales agreements with our customers are fixed-priced, fixed-volume supply contracts, or include a predetermined escalation in price for each year. Price re-opener and index provisions may allow either party to commence a renegotiation of the contract price at a pre-determined time. Price re-opener provisions may automatically set a new price based on prevailing market price or, in some instances, require us to negotiate a new price, sometimes within specified ranges of prices. The terms of our coal sales agreements result from competitive bidding and extensive negotiations with customers. Consequently, the terms of these contracts vary by customer. Coal sales agreements will typically contain coal quality specifications. With coal quality specifications in place, the raw coal sold by us to the customer at the delivery point must be substantially free of magnetic material and other foreign material impurities and crushed to a maximum size as set forth in the respective coal sales agreement. Price adjustments are made and billed in the month the coal sale was recognized based on quality standards that are specified in the coal sales agreement, such as Btu factor, moisture, ash, and sulfur content and can result in either increases or decreases in the value of the coal shipped. Disaggregation of Revenue Revenue is disaggregated by primary geographic markets, as we believe this best depicts how the nature, amount, timing, and uncertainty of our revenue and cash flows are affected by economic factors. 72% and 74% of our coal revenue for the three months ended March 31, 2019 and 2018, respectively, was sold to customers in the State of Indiana with the remainder sold to customers in Florida, Georgia, North Carolina, Kentucky, Tennessee, and South Carolina. Performance Obligations A performance obligation is a promise in a contract with a customer to provide distinct goods or services. Performance obligations are the unit of account for purposes of applying the revenue recognition standard and therefore determine when and how revenue is recognized. In most of our contracts, the customer contracts with us to provide coal that meets certain quality criteria. We consider each ton of coal a separate performance obligation and allocate the transaction price based on the base price per the contract, increased or decreased for quality adjustments. We recognize revenue at a point in time as the customer does not have control over the asset at any point during the fulfillment of the contract. For substantially all of our customers, this is supported by the fact that title and risk of loss transfer to the customer upon loading of the truck or railcar at the mine. This is also the point at which physical possession of the coal transfers to the customer, as well as the right to receive substantially all benefits and the risk of loss in ownership of the coal. We have remaining performance obligations relating to fixed priced contracts of approximately $756 million, which represent the average fixed prices on our committed contracts as of March 31, 2019. We expect to recognize approximately 65% of this revenue through 2020, with the remainder recognized thereafter. We have remaining performance obligations relating to index priced contracts or contracts with price reopeners of approximately $330 million, which represents our estimate of the expected re-opener/indexed price on committed contracts as of March 31, 2019. We expect to recognize all of this income beginning in 2020. The tons used to determine the remaining performance obligations are subject to adjustment in instances of force majeure and exercise of customer options to either take additional tons or reduce tonnage if such option exists in the customer contract. Contract Balances Under ASC 606, the timing of when a performance obligation is satisfied can affect the presentation of accounts receivable, contract assets, and contract liabilities. The main distinction between accounts receivable and contract assets is whether consideration is conditional on something other than the passage of time. A receivable is an entity’s right to consideration that is unconditional. Under the typical payment terms of our contracts with customers, the customer pays us a base price for the coal, increased or decreased for any quality adjustments. Amounts billed and due are recorded as trade accounts receivable and included in accounts receivable in our consolidated balance sheets. We do not currently have any contracts in place where we would transfer coal in advance of knowing the final price of the coal sold, and thus do not have any contract assets recorded. Contract liabilities arise when consideration is received in advance of performance. This deferred revenue is included in accounts payable and accrued liabilities in our consolidated balance sheets when consideration is received, and revenue is not recognized until the performance obligation is satisfied. We are rarely paid in advance of performance and do not currently have any deferred revenue recorded in our consolidated balance sheets.

(12)REVENUE

Effective January 1, 2018, we adopted ASU 2014-09. The adoption of this standard did not impact the timing of revenue recognition on our consolidated balance sheets or condensed consolidated statements of comprehensive income.

Revenue from Contracts with Customers

We account for a contract with a customer when the parties have approved the contract and are committed to performing their respective obligations, the rights of each party are identified, payment terms are identified, the contract has commercial substance, and collectability of consideration is probable. We recognize revenue when we satisfy a performance obligation by transferring control of a good or service to a customer.

Our revenue is derived from sales to customers of coal produced at our facilities. Our customers purchase coal directly from our mine sites and our Princeton Loop, where the sale occurs and where title, risk of loss, and control typically pass to the customer at that point. Our customers arrange for and bear the costs of transporting their coal from our mines to their plants or other specified discharge points. Our customers are typically domestic utility companies. Our coal sales agreements with our customers are fixed-priced, fixed-volume supply contracts, or include a predetermined escalation in price for each year. Price re-opener and index provisions may allow either party to commence a renegotiation of the contract price at a pre-determined time. Price re-opener provisions may automatically set a new price based on prevailing market price or, in some instances, require us to negotiate a new price, sometimes within specified ranges of prices. The terms of our coal sales agreements result from competitive bidding and extensive negotiations with customers. Consequently, the terms of these contracts vary by customer.

Coal sales agreements will typically contain coal quality specifications. With coal quality specifications in place, the raw coal sold by us to the customer at the delivery point must be substantially free of magnetic material and other foreign material impurities and crushed to a maximum size as set forth in the respective coal sales agreement. Price adjustments are made and billed in the month the coal sale was recognized based on quality standards that are specified in the coal sales agreement, such as Btu factor, moisture, ash, and sulfur content and can result in either increases or decreases in the value of the coal shipped.

Disaggregation of Revenue

Revenue is disaggregated by primary geographic markets, as we believe this best depicts how the nature, amount, timing, and uncertainty of our revenue and cash flows are affected by economic factors. 72% and 74% of our coal revenue for the three months ended March 31, 2019 and 2018, respectively, was sold to customers in the State of Indiana with the remainder sold to customers in Florida, Georgia, North Carolina, Kentucky, Tennessee, and South Carolina.

Performance Obligations

A performance obligation is a promise in a contract with a customer to provide distinct goods or services. Performance obligations are the unit of account for purposes of applying the revenue recognition standard and therefore determine when and how revenue is recognized. In most of our contracts, the customer contracts with us to provide coal that meets certain quality criteria. We consider each ton of coal a separate performance obligation and allocate the transaction price based on the base price per the contract, increased or decreased for quality adjustments.

We recognize revenue at a point in time as the customer does not have control over the asset at any point during the fulfillment of the contract. For substantially all of our customers, this is supported by the fact that title and risk of loss transfer to the customer upon loading of the truck or railcar at the mine. This is also the point at which physical possession of the coal transfers to the customer, as well as the right to receive substantially all benefits and the risk of loss in ownership of the coal.

We have remaining performance obligations relating to fixed priced contracts of approximately $756 million, which represent the average fixed prices on our committed contracts as of March 31, 2019. We expect to recognize approximately 65% of this revenue through 2020, with the remainder recognized thereafter. We have remaining performance obligations relating to index priced contracts or contracts with price reopeners of approximately $330 million, which represents our estimate of the expected re-opener/indexed price on committed contracts as of March 31, 2019. We expect to recognize all of this income beginning in 2020.

The tons used to determine the remaining performance obligations are subject to adjustment in instances of force majeure and exercise of customer options to either take additional tons or reduce tonnage if such option exists in the customer contract.

Contract Balances

Under ASC 606, the timing of when a performance obligation is satisfied can affect the presentation of accounts receivable, contract assets, and contract liabilities. The main distinction between accounts receivable and contract assets is whether consideration is conditional on something other than the passage of time. A receivable is an entity’s right to consideration that is unconditional. Under the typical payment terms of our contracts with customers, the customer pays us a base price for the coal, increased or decreased for any quality adjustments. Amounts billed and due are recorded as trade accounts receivable and included in accounts receivable in our consolidated balance sheets. We do not currently have any contracts in place where we would transfer coal in advance of knowing the final price of the coal sold, and thus do not have any contract assets recorded. Contract liabilities arise when consideration is received in advance of performance. This deferred revenue is included in accounts payable and accrued liabilities in our consolidated balance sheets when consideration is received, and revenue is not recognized until the performance obligation is satisfied. We are rarely paid in advance of performance and do not currently have any deferred revenue recorded in our consolidated balance sheets.