Aggregate Positions in Capital Structure of Borrowers (Detail) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015	[1]
Schedule of Held-to-maturity Securities [Line Items]
Corporate debt, total	$ 639,481	$ 488,508
Subordinated Debt [Member]
Schedule of Held-to-maturity Securities [Line Items]
Corporate debt, total	4,359
First Lien [Member]
Schedule of Held-to-maturity Securities [Line Items]
Corporate debt, total	397,693
Second Lien [Member]
Schedule of Held-to-maturity Securities [Line Items]
Corporate debt, total	162,729
Corporate Debt Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Corporate debt, total	$ 74,700

[1] Derived from the audited consolidated financial statements at December 31, 2015.