Fair Value Measurements and Disclosures, Investment Percentages (Details)	Dec. 31, 2012	Dec. 31, 2011
TT II, LLC [Member]
Ownership Interests [Line Items]
Percentage of investment in trading companies (in hundredths)	34.90%	26.80%
WNT I, LLC [Member]
Ownership Interests [Line Items]
Percentage of investment in trading companies (in hundredths)	20.15%	17.00%
Kaiser I, LLC [Member]
Ownership Interests [Line Items]
Percentage of investment in trading companies (in hundredths)	9.10%	20.05%
Rotella I, LLC [Member]
Ownership Interests [Line Items]
Percentage of investment in trading companies (in hundredths)	9.65%	9.65%
Augustus I, LLC [Member]
Ownership Interests [Line Items]
Percentage of investment in trading companies (in hundredths)	6.95%	9.70%
GLC I, LLC [Member]
Ownership Interests [Line Items]
Percentage of investment in trading companies (in hundredths)	6.70%	7.50%
Chesapeake I, LLC [Member]
Ownership Interests [Line Items]
Percentage of investment in trading companies (in hundredths)	12.55%	9.30%