Inventories (Details) $ in Thousands, bu in Millions	Sep. 30, 2017 USD ($) bu	Dec. 31, 2016 USD ($) bu	Sep. 30, 2016 USD ($) bu
Inventory, Net [Abstract]
Grain	$ 342,837	$ 495,139	$ 262,165
Ethanol and co-products	12,502	10,887	7,734
Plant nutrients and cob products	114,131	150,259	126,922
Retail merchandise	718	20,678	24,985
Railcar repair parts	5,414	5,784	5,948
Total inventories	$ 475,602	$ 682,747	$ 427,754
Bushels of grain held in storage and excluded from inventory calculations | bu	1.0	0.9	1.0