Exit Costs and Assets Held for Sale (Details) - USD ($) $ in Thousands	3 Months Ended
	Jun. 30, 2017	Dec. 31, 2017	Dec. 31, 2016
Restructuring Cost and Reserve [Line Items]
Assets held for sale		$ 37,859	$ 0
Retail Business
Restructuring Cost and Reserve [Line Items]
Business exit costs	$ 11,500
Disposal Group, Held-for-sale, Not Discontinued Operations | Grain Group | TENNESSEE
Restructuring Cost and Reserve [Line Items]
Assets held for sale		37,900
Property, plant and equipment, held for sale		19,500
Inventories, held for sale		11,400
Commodity derivative asset, held for sale		1,200
Disposal Group, Held-for-sale, Not Discontinued Operations | Retail Store
Restructuring Cost and Reserve [Line Items]
Property, plant and equipment, held for sale		4,200
Disposal Group, Held-for-sale, Not Discontinued Operations | Plant Nutrient Group
Restructuring Cost and Reserve [Line Items]
Property, plant and equipment, held for sale		$ 1,600