Summary of Financial Instruments for Which Fair Value Option Has Been Elected (Detail) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity and Preferred Securities	$ 280,028	$ 280,879
Total Assets	4,358,240	4,024,612
Total Liabilities	3,554,019	3,323,435
Corporate Bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets of Consolidated CLO Vehicles: Corporate Bonds	412,073	379,000
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	3,467,956	3,225,064
Subordinated Notes | Liabilities of Consolidated CLO Vehicles
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of Notes	86,063	98,371
Loans and Receivables
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans and Receivables	287,858	261,994
Debt Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Securities	14,487	15,176
Corporate Loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets of Consolidated CLO Vehicles: Corporate Loans	$ 3,363,794	$ 3,087,563