Investments - Schedule of Company's Investments in Limited Partnerships (Parenthetical) (Detail) $ in Thousands	6 Months Ended
	Jun. 30, 2020 USD ($)
Schedule Of Investments [Line Items]
Additional funding circumstances	$ 843
Private US Lower Middle Market Companies [Member]
Schedule Of Investments [Line Items]
Expected term	10 years
Investment additional maturity term	2 years
Bank Loans Public and Private Corporate Bonds Asset Backed Securities Equity and Debt Restructuring [Member]
Schedule Of Investments [Line Items]
Expected term	3 years
Investment additional maturity term	2 years
Power Utility and Energy Industries and Infrastructure [Member]
Schedule Of Investments [Line Items]
Expected term	10 years
Investment additional maturity term	3 years
Senior and Junior Debts of Private Equity-Backed Companies [Member]
Schedule Of Investments [Line Items]
Expected term	6 years
Investment additional maturity term	2 years
Expiration date of capital commitment	Dec. 01, 2020
Mature Real Estate Private Equity Funds And Portfolio Globally [Member]
Schedule Of Investments [Line Items]
Expected term	8 years