Fair Value Measurements and Disclosures, Investment Percentages (Details)	Dec. 31, 2014	Dec. 31, 2013
TT II, LLC [Member]
Ownership Interests [Line Items]
Percentage of investment in trading companies (in hundredths)	32.70%	27.65%
WNT I, LLC [Member]
Ownership Interests [Line Items]
Percentage of investment in trading companies (in hundredths)		16.95%
Kaiser I, LLC [Member]
Ownership Interests [Line Items]
Percentage of investment in trading companies (in hundredths)		8.30%
Rotella I, LLC [Member]
Ownership Interests [Line Items]
Percentage of investment in trading companies (in hundredths)		17.95%
Augustus I, LLC [Member]
Ownership Interests [Line Items]
Percentage of investment in trading companies (in hundredths)	38.30%	19.20%
Boronia I, LLC [Member]
Ownership Interests [Line Items]
Percentage of investment in trading companies (in hundredths)	29.00%	9.95%