CORPORATE LOANS AND ALLOWANCE FOR LOAN LOSSES (Details 7) (USD $)	3 Months Ended	12 Months Ended
	Mar. 31, 2013	Dec. 31, 2012
Texas Competitive Electric Holdings Company LLC, Modular Space Corporation, and U.S. Foodservice
Concentrated risks
Concentration risk of total amortized cost basis (as a percent)	16.00%	16.00%
Amortized cost of corporate loans concentrated in major issuers	$ 996,700,000	$ 1,000,000,000
Corporate Loans
Concentrated risks
Number of issuers with whom a specified percentage of amortized cost of corporate loans is concentrated	20	20
Number of issuers with the largest concentration of corporate loans	3	3
Corporate Loans | Percent to Total Corporate Loans
Concentrated risks
Concentration risk of total amortized cost basis (as a percent)	48.00%	46.00%
Corporate Loans, at Estimated Fair Value
Concentrated risks
Pledged as collateral for collateralized loan obligation secured debt and junior secured notes to affiliates	$ 0	$ 0