Investments - Summary of Investments in Fair Value Hierarchy Levels (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Assets, at fair value:
Total	$ 1,736,703	$ 1,744,412
AAA Investments [Member]
Assets, at fair value:
Total	1,659,093	1,666,448
Investments held by Apollo Senior Loan Fund [Member]
Assets, at fair value:
Total	27,218	27,653
Investments in HFA and Other [Member]
Assets, at fair value:
Total	50,392	50,311
Level II [Member]
Assets, at fair value:
Total	26,781	27,063
Level II [Member] | Investments held by Apollo Senior Loan Fund [Member]
Assets, at fair value:
Total	26,781	27,063
Level III [Member]
Assets, at fair value:
Total	1,709,922	1,717,349
Level III [Member] | AAA Investments [Member]
Assets, at fair value:
Total	1,659,093	1,666,448
Level III [Member] | Investments held by Apollo Senior Loan Fund [Member]
Assets, at fair value:
Total	437	590
Level III [Member] | Investments in HFA and Other [Member]
Assets, at fair value:
Total	$ 50,392	$ 50,311