Related Party Transactions (Bunge) (Narrative) (Details) bu in Thousands		1 Months Ended	3 Months Ended	12 Months Ended
	Jun. 26, 2009	Jan. 31, 2015	Dec. 31, 2016	Sep. 30, 2019 USD ($) bu	Sep. 30, 2018 USD ($) bu
Related Party Transaction [Line Items]
Revenues				$ 216,993,000	$ 214,990,000
Accounts Receivable, Related Parties, Current				7,885,000	11,537,000
Bunge [Member]
Related Party Transaction [Line Items]
Marketing Expense				2,800,000	2,700,000
Revenues				205,100,000	204,700,000
Accounts Receivable, Related Parties, Current				7,900,000	11,600,000
Ethanol Agreement [Member] | Bunge [Member]
Related Party Transaction [Line Items]
Investment from related parties				$ 1,500,000	1,535,138
Renewal period				5 years
Railcar Agreement [Member] | Bunge [Member]
Related Party Transaction [Line Items]
Agreement period		120 months
Related Party Transaction, Expenses from Transactions with Related Party				$ 3,500,000	$ 4,000,000.0
Railcar Agreement [Member] | Ethanol Cars [Member] | Bunge [Member]
Related Party Transaction [Line Items]
Number Of Railcars	325		323	323
Agreement period				4 years
Railcar Agreement [Member] | Hopper Cars [Member] | Bunge [Member]
Related Party Transaction [Line Items]
Number Of Railcars	300	298		111
Railcar lease reduction		1			1
Agreement period				3 years
Sublease, hopper car, units				96
Railcar Agreement [Member] | Hopper Cars [Member] | Unrelated Party [Member]
Related Party Transaction [Line Items]
Sublease, hopper car, units				92
Assignment, hopper cars, unit				52
Distillers Grain Purchase Agreement [Member] | Bunge [Member]
Related Party Transaction [Line Items]
Marketing Expense				$ 1,300,000	$ 1,200,000
Renewal period				5 years
Grain Feedstock Agency Agreement [Member] | Bunge [Member]
Related Party Transaction [Line Items]
Investment from related parties				$ 700,000	$ 720,000
Derivative Contracts, Corn, Bushels | bu				7	116
Derivative Contracts, Corn, Dollars				$ 25,000	$ 393,000
Renewal period				5 years
Services Agreement [Member] | Bunge [Member]
Related Party Transaction [Line Items]
Renewal period				5 years