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		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Realized 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		$ (1,554)		$ (4,092)
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	$ (8,300)	(32,119)	$ (1,690)	(54,850)
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	91	(3,284)	121	(2,186)
Realized 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		(1,554)		(4,092)
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	1,318	(1,703)	3,273	13,294
Realized Gains (Losses) | Equity and Preferred 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	(52)	(739)	(237)	(1,323)
Realized Gains (Losses) | Corporate Loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Realized and net change in unrealized gains (losses) on financial instruments	(9,657)	(26,393)	(4,847)	(64,635)
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	(7,199)	(21,105)	(10,238)	(40,024)
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	20,450	60,809	33,978	78,120
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	3,380	3,442	4,516	3,694
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		(39,764)		(95,638)
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	(7,199)	18,659	(10,238)	55,614
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	(840)	22,673	(3,331)	19,555
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	1,278		(597)
Net Change In Unrealized Gains (Losses) | Equity and Preferred 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	(4,663)	796	(7,491)	5,914
Net Change In Unrealized Gains (Losses) | Corporate Loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Realized and net change in unrealized gains (losses) on financial instruments	$ 21,295	$ 33,898	$ 40,881	$ 48,957