Variable Interest Entities - Summary of Assets and Liabilities of Consolidated CLO and Single Asset Securitization VIE (Detail) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Assets:
Assets	$ 20,705,872	$ 16,958,955
Liabilities:
Liabilities	16,435,320	13,054,724
VIE [Member]
Assets:
Assets	3,503,362	3,587,950
Liabilities:
Liabilities	2,837,680	2,924,603
VIE [Member] | Loans Receivable [Member]
Assets:
Assets	3,475,000	3,520,130
Loans receivable, net	3,470,956	3,506,676
VIE [Member] | Current Expected Credit Loss Reserve [Member]
Assets:
Assets	(4,044)	(13,454)
VIE [Member] | Other Assets [Member]
Assets:
Assets	32,406	81,274
VIE [Member] | Securitized Debt Obligations, Net [Member]
Liabilities:
Liabilities	2,836,049	2,922,499
VIE [Member] | Other Liabilities [Member]
Liabilities:
Liabilities	$ 1,631	$ 2,104