Inventories (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Inventories
Crude oil and petroleum products	$ 465,000	$ 418,000
Materials and supplies	558,000	600,000
Total Inventories	1,023,000	1,018,000
Inventories (Textual) [Abstract]
Inventories valued on the LIFO basis	297,000	269,000
Excess of current replacement cost over LIFO cost of inventories	$ 90,000	$ 104,000