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	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Realized Gains (Losses) | Debt Securities
Fair Value, Option, Quantitative Disclosures [Line Items]
Realized and net change in unrealized gains (losses) on financial instruments	$ (22,240)	$ 14,399	$ (22,783)
Realized Gains (Losses) | Assets
Fair Value, Option, Quantitative Disclosures [Line Items]
Realized and net change in unrealized gains (losses) on financial instruments	(10,688)	45,529	(129,633)
Realized Gains (Losses) | Loans and Receivables
Fair Value, Option, Quantitative Disclosures [Line Items]
Realized and net change in unrealized gains (losses) on financial instruments	(10,733)	(11,661)	(10,314)
Realized Gains (Losses) | Equity and Preferred Securities
Fair Value, Option, Quantitative Disclosures [Line Items]
Realized and net change in unrealized gains (losses) on financial instruments	22,285	42,791	(342)
Realized Gains (Losses) | Corporate Loans
Fair Value, Option, Quantitative Disclosures [Line Items]
Realized and net change in unrealized gains (losses) on financial instruments			(96,194)
Net Change In Unrealized Gains (Losses) | Debt Securities
Fair Value, Option, Quantitative Disclosures [Line Items]
Realized and net change in unrealized gains (losses) on financial instruments	(19,490)	(14,210)	29,143
Net Change In Unrealized Gains (Losses) | Assets
Fair Value, Option, Quantitative Disclosures [Line Items]
Realized and net change in unrealized gains (losses) on financial instruments	(111,292)	42,428	(267,604)
Net Change In Unrealized Gains (Losses) | Loans and Receivables
Fair Value, Option, Quantitative Disclosures [Line Items]
Realized and net change in unrealized gains (losses) on financial instruments	(464)	3,481	(2,011)
Net Change In Unrealized Gains (Losses) | Liabilities
Fair Value, Option, Quantitative Disclosures [Line Items]
Realized and net change in unrealized gains (losses) on financial instruments	(7,508)	(383)	229,247
Net Change In Unrealized Gains (Losses) | Equity and Preferred Securities
Fair Value, Option, Quantitative Disclosures [Line Items]
Realized and net change in unrealized gains (losses) on financial instruments	(91,338)	53,157	(67,869)
Net Change In Unrealized Gains (Losses) | Corporate Loans
Fair Value, Option, Quantitative Disclosures [Line Items]
Realized and net change in unrealized gains (losses) on financial instruments			(226,542)
Net Change In Unrealized Gains (Losses) | Senior Secured Notes
Fair Value, Option, Quantitative Disclosures [Line Items]
Realized and net change in unrealized gains (losses) on financial instruments			199,445
Net Change In Unrealized Gains (Losses) | Subordinated Notes
Fair Value, Option, Quantitative Disclosures [Line Items]
Realized and net change in unrealized gains (losses) on financial instruments			30,046
Net Change In Unrealized Gains (Losses) | Corporate Treasury Commitments
Fair Value, Option, Quantitative Disclosures [Line Items]
Realized and net change in unrealized gains (losses) on financial instruments	$ (7,508)	$ (383)	(244)
Net Change In Unrealized Gains (Losses) | Other
Fair Value, Option, Quantitative Disclosures [Line Items]
Realized and net change in unrealized gains (losses) on financial instruments			$ (325)