Revenue Recognition We derive our revenues by mining, manufacturing, and processing minerals that our customers purchase for various uses. Revenues are primarily derived from contracts with customers with terms typically ranging from one to eight years in length, and are measured by the amount of consideration we expect to receive in exchange for transferring our products. The consideration we expect to receive is based on the volumes and price of the product per ton as defined in the underlying contract. The price per ton is based on the market value for similar products plus costs associated with transportation and transloading, as applicable. Depending on the contract, this may also be net of discounts and rebates. The transaction price is not adjusted for the effects of a significant financing component, as the time period between transfer of control of the goods and expected payment is one year or less. Sales, value-added, and other similar taxes collected are excluded from revenue. On January 1, 2018, we adopted ASU No. 2014-09  Revenue from Contracts with Customers (Topic 606) . The adoption did not require a cumulative adjustment to opening retained earnings and did not have a material impact on revenues for the year ended December 31, 2018. Revenues are recognized as each performance obligation within the contract is satisfied; this occurs with the transfer of control of our product in accordance with delivery methods as defined in the underlying contract. Transfer of control to customers generally occurs when products leave our facilities or at other predetermined control transfer points. We have elected to continue to account for shipping and handling activities that occur after control of the related good transfers, as a cost of fulfillment instead of a separate performance obligation. Transportation costs to move product from our production facilities to our distribution terminals are borne by us and capitalized into inventory. These costs are included in cost of goods sold as the products are sold. Our contracts may include one or multiple distinct performance obligations. Revenues are assigned to each performance obligation based on its relative standalone selling price, which is generally the contractually-stated price. Our products may be sold with rebates, discounts, take-or-pay provisions, or other features which are accounted for as variable consideration. Rebates and discounts are not material and have not been separately disclosed. Contracts that contain take-or-pay provisions obligate customers to pay shortfall payments if the required volumes, as defined in the contracts, are not purchased. Shortfall payments are recognized as revenues when the likelihood of the customer purchasing the minimum volume becomes remote, subject to renegotiation of the contract and collectability. At March 31, 2019 and December 31, 2018, we had no accounts receivable related to shortfall payments. We disaggregate revenues by major source consistent with our segment reporting. See Note 18 for further detail.