Realized and Net Change in Unrealized Gains (Losses) on Financial Instruments on Financial Instruments on Which Fair Value Option was Elected (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Realized Gains (Losses) | Assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Realized and net change in unrealized gains (losses) on financial instruments	$ (13,336)	$ (5,408)
Realized Gains (Losses) | Corporate Bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Realized and net change in unrealized gains (losses) on financial instruments	190	30
Realized Gains (Losses) | Other
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Realized and net change in unrealized gains (losses) on financial instruments	178	1,955
Net Change In Unrealized Gains (Losses) | Liabilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Realized and net change in unrealized gains (losses) on financial instruments	12,413	(3,040)
Net Change In Unrealized Gains (Losses) | Loans and Receivables
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Realized and net change in unrealized gains (losses) on financial instruments	(3,778)	(1,875)
Net Change In Unrealized Gains (Losses) | Debt Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Realized and net change in unrealized gains (losses) on financial instruments	(689)
Net Change In Unrealized Gains (Losses) | Assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Realized and net change in unrealized gains (losses) on financial instruments	(7,071)	16,498
Net Change In Unrealized Gains (Losses) | Corporate Bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Realized and net change in unrealized gains (losses) on financial instruments	271	1,135
Net Change In Unrealized Gains (Losses) | Senior Secured Notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Realized and net change in unrealized gains (losses) on financial instruments		(3,794)
Net Change In Unrealized Gains (Losses) | Subordinated Notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Realized and net change in unrealized gains (losses) on financial instruments	12,413	754
Net Change In Unrealized Gains (Losses) | Other
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Realized and net change in unrealized gains (losses) on financial instruments		(2,491)
Equity and Preferred Securities | Realized Gains (Losses)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Realized and net change in unrealized gains (losses) on financial instruments	3	(185)
Equity and Preferred Securities | Net Change In Unrealized Gains (Losses)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Realized and net change in unrealized gains (losses) on financial instruments	(3,832)	(2,828)
Corporate Loans | Realized Gains (Losses)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Realized and net change in unrealized gains (losses) on financial instruments	(13,707)	(7,208)
Corporate Loans | Net Change In Unrealized Gains (Losses)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Realized and net change in unrealized gains (losses) on financial instruments	$ 957	$ 22,557