Related Party Transactions (Bunge) (Narrative) (Details) $ / shares in Units, $ in Millions	3 Months Ended			6 Months Ended
	Mar. 31, 2019 USD ($) $ / shares Rate shares	Mar. 31, 2018 USD ($)	Dec. 31, 2014	Mar. 31, 2019 USD ($) a $ / shares shares	Mar. 31, 2018 USD ($)
Related Party Transaction [Line Items]
Share repurchase agreement, minimum per share price | $ / shares	$ 10,897			$ 10,897
Railcar Agreement [Member]
Related Party Transaction [Line Items]
Agreement period				120 months
Bunge [Member] | DG Agreement [Member]
Related Party Transaction [Line Items]
Total Renewal Periods				1
Related Party Renewal Period				5 years
Minimum renewal notice time				180 days
Related Party Transaction, Expenses from Transactions with Related Party	$ 0.3	$ 0.3		$ 0.7	$ 0.6
Bunge [Member] | Grain Feedstock Agency Agreement [Member]
Related Party Transaction [Line Items]
Total Renewal Periods				1
Related Party Renewal Period				5 years
Minimum renewal notice time				180 days
Related Party Transaction, Expenses from Transactions with Related Party	0.2	0.2		$ 0.4	0.4
Bunge [Member] | Ethanol Agreement [Member]
Related Party Transaction [Line Items]
Total Renewal Periods				1
Related Party Renewal Period				5 years
Minimum renewal notice time				180 days
Related Party Transaction, Expenses from Transactions with Related Party	0.4	0.4		$ 0.8	0.8
Bunge [Member] | Services Agreement [Member]
Related Party Transaction [Line Items]
Total Renewal Periods				1
Related Party Renewal Period				5 years
Minimum renewal notice time				180 days
Contracted Acres, Enogen | a				25,500
Bunge [Member] | Railcar Agreement [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Expenses from Transactions with Related Party	$ 1.0	$ 1.0		$ 1.9	$ 2.0
Lease Expense Reduction | Rate	25.00%
number of railcars, subleased				96
Other unrelated parties [Member]
Related Party Transaction [Line Items]
number of railcars, subleased				40
Other unrelated parties [Member] | Railcar Agreement [Member]
Related Party Transaction [Line Items]
number of railcars, subleased				52
Ethanol Cars [Member] | Extended Railcar Agreement [Member]
Related Party Transaction [Line Items]
Number of railcars				323
Ethanol Cars [Member] | Railcar Agreement [Member]
Related Party Transaction [Line Items]
Number of railcars			325	323
Hopper Cars [Member] | Extended Railcar Agreement [Member]
Related Party Transaction [Line Items]
Number of railcars				111
Hopper Cars [Member] | Railcar Agreement [Member]
Related Party Transaction [Line Items]
Number of railcars			300	298
Common Class C [Member]
Related Party Transaction [Line Items]
Stock Repurchase Program, Number of Shares Authorized to be Repurchased | shares	1,000			1,000
Common Class A [Member]
Related Party Transaction [Line Items]
Stock Repurchase Program, Number of Shares Authorized to be Repurchased | shares	18			18