Fair Value Measurements and Disclosures, Investment Percentages (Details)	Dec. 31, 2013	Dec. 31, 2012
Aspect I, LLC [Member]
Other Ownership Interests [Line Items]
Percentage of investment in trading companies (in hundredths)	14.25%	17.40%
Kaiser I, LLC [Member]
Other Ownership Interests [Line Items]
Percentage of investment in trading companies (in hundredths)	9.50%
AHL I, LLC [Member]
Other Ownership Interests [Line Items]
Percentage of investment in trading companies (in hundredths)		18.90%
Altis I, LLC [Member]
Other Ownership Interests [Line Items]
Percentage of investment in trading companies (in hundredths)	24.05%	20.20%
BHM I, LLC [Member]
Other Ownership Interests [Line Items]
Percentage of investment in trading companies (in hundredths)	39.75%	35.85%
Boronia I, LLC [Member]
Other Ownership Interests [Line Items]
Percentage of investment in trading companies (in hundredths)	12.45%	7.65%