Aggregate Positions in Capital Structure of Borrowers (Detail) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015	[1]
Schedule of Held-to-maturity Securities [Line Items]
Corporate debt, total	$ 669,612	$ 488,508
Subordinated Debt [Member]
Schedule of Held-to-maturity Securities [Line Items]
Corporate debt, total	4,369
First Lien [Member]
Schedule of Held-to-maturity Securities [Line Items]
Corporate debt, total	418,972
Second Lien [Member]
Schedule of Held-to-maturity Securities [Line Items]
Corporate debt, total	161,862
Corporate Debt Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Corporate debt, total	$ 84,409

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