Fair Value Measurements and Disclosures, Investment Percentages (Details)	Sep. 30, 2013	Dec. 31, 2012
TT II, LLC [Member]
Ownership Interests [Line Items]
Percentage of investment in trading companies (in hundredths)	29.50%	34.90%
Augustus I, LLC [Member]
Ownership Interests [Line Items]
Percentage of investment in trading companies (in hundredths)	20.40%	6.95%
WNT I, LLC [Member]
Ownership Interests [Line Items]
Percentage of investment in trading companies (in hundredths)	17.15%	20.15%
Boronia I, LLC [Member]
Ownership Interests [Line Items]
Percentage of investment in trading companies (in hundredths)	9.00%
Rotella I, LLC [Member]
Ownership Interests [Line Items]
Percentage of investment in trading companies (in hundredths)	16.30%	9.65%
Kaiser I, LLC [Member]
Ownership Interests [Line Items]
Percentage of investment in trading companies (in hundredths)	7.65%	9.10%
Chesapeake I, LLC [Member]
Ownership Interests [Line Items]
Percentage of investment in trading companies (in hundredths)		12.55%
GLC I, LLC [Member]
Ownership Interests [Line Items]
Percentage of investment in trading companies (in hundredths)		6.70%