Summary of Financial Instruments for Which Fair Value Option Has Been Elected (Detail) - Entity [Domain] - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity and Preferred Securities	$ 127,191	$ 102,907
Total Assets	3,425,835	6,760,099
Total Liabilities	3,032,330	6,797,104
Corporate Bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets of Consolidated CLO Vehicles: Corporate Bonds	247,083	292,690
Senior Secured Notes | Liabilities of Consolidated CLO Vehicles
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of Notes	2,912,753	6,448,352
Subordinated Notes | Liabilities of Consolidated CLO Vehicles
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of Notes	119,577	348,752
Other
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets of Consolidated CLO Vehicles: Other	281	44,513
Loans And Receivables
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans and Receivables	36,440	40,397
Corporate Loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets of Consolidated CLO Vehicles: Corporate Loans	$ 3,014,840	$ 6,279,592