Inventories	9 Months Ended
Sep. 30, 2017
Inventory Disclosure [Abstract]
Inventories	5. Inventories Inventories are valued at the lower of cost or market for last-in, first-out (“LIFO”) inventory and lower of cost or net realizable value for first-in, first-out (“FIFO”) inventory. Approximately 40 percent of our inventories are valued using the LIFO method of determining cost. All other inventories are valued at the FIFO method of determining cost. An actual valuation of inventory under the LIFO method can be made only at the end of each year based on inventory levels and costs at that time. Accordingly, interim LIFO calculations must necessarily be based on management’s estimates of expected year-end inventory levels and costs. Because these are based on estimates, interim results are subject to change in the final year-end LIFO inventory valuation. In the current quarter, one inventory pool had an increase in commodity costs that is expected to hold through year-end, and therefore, an adjustment of $0.4 million was made to increase the LIFO reserve and cost of sales for the three months ended September 30, 2017. No adjustment was recorded during prior interim reporting periods as interim results in those periods were immaterial.

5. Inventories

Inventories are valued at the lower of cost or market for last-in, first-out (“LIFO”) inventory and lower of cost or net realizable value for first-in, first-out (“FIFO”) inventory. Approximately 40 percent of our inventories are valued using the LIFO method of determining cost. All other inventories are valued at the FIFO method of determining cost. An actual valuation of inventory under the LIFO method can be made only at the end of each year based on inventory levels and costs at that time. Accordingly, interim LIFO calculations must necessarily be based on management’s estimates of expected year-end inventory levels and costs. Because these are based on estimates, interim results are subject to change in the final year-end LIFO inventory valuation. In the current quarter, one inventory pool had an increase in commodity costs that is expected to hold through year-end, and therefore, an adjustment of $0.4 million was made to increase the LIFO reserve and cost of sales for the three months ended September 30, 2017. No adjustment was recorded during prior interim reporting periods as interim results in those periods were immaterial.