Disclosures About Fair Value of Financial Instruments (Details) Notional Amounts of Derivatives	Mar. 31, 2013 T
Exchange Traded | Agricultural Commodities Futures | Short
Derivatives, Fair Value [Line Items]
Notional amount of nonmonetary derivative	(37,258,000)	[1]
Exchange Traded | Agricultural Commodities Futures | Long
Derivatives, Fair Value [Line Items]
Notional amount of nonmonetary derivative	43,270,000	[1]
Exchange Traded | Natural Gas Futures | Long
Derivatives, Fair Value [Line Items]
Notional amount of nonmonetary derivative	37,500,000	[1]
Non-Exchange Traded | Forwards | Short
Derivatives, Fair Value [Line Items]
Notional amount of nonmonetary derivative	(134,331,000)	[1]
Non-Exchange Traded | Forwards | Long
Derivatives, Fair Value [Line Items]
Notional amount of nonmonetary derivative	32,673,000	[1]
Non-Exchange Traded | Swaps | Long
Derivatives, Fair Value [Line Items]
Notional amount of nonmonetary derivative	30,000	[1]

[1] Exchange and non-exchange traded futures, forwards, and swaps are presented on a gross (short) and long position basis.