Fair Value Measurements and Disclosures, Investment Percentages (Details)	Mar. 31, 2013	Dec. 31, 2012
TT II, LLC [Member]
Ownership Interests [Line Items]
Percentage of investment in trading companies (in hundredths)	28.50%	34.90%
WNT I, LLC [Member]
Ownership Interests [Line Items]
Percentage of investment in trading companies (in hundredths)	18.25%	20.15%
Boronia I, LLC [Member]
Ownership Interests [Line Items]
Percentage of investment in trading companies (in hundredths)	7.75%
Rotella I, LLC [Member]
Ownership Interests [Line Items]
Percentage of investment in trading companies (in hundredths)	13.60%	9.65%
Kaiser I, LLC [Member]
Ownership Interests [Line Items]
Percentage of investment in trading companies (in hundredths)	7.05%	9.10%
Augustus I, LLC [Member]
Ownership Interests [Line Items]
Percentage of investment in trading companies (in hundredths)	13.25%	6.95%
Chesapeake I, LLC [Member]
Ownership Interests [Line Items]
Percentage of investment in trading companies (in hundredths)	11.60%	12.55%
GLC I, LLC [Member]
Ownership Interests [Line Items]
Percentage of investment in trading companies (in hundredths)		6.70%