Investments - Schedule of Company's Investments in Limited Partnerships (Detail) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2020	Dec. 31, 2019
Investment Securities [Line Items]
Carrying Value	$ 26,177	$ 28,346
Unfunded Balance	13,660	15,130
Private US Lower Middle Market Companies [Member]
Investment Securities [Line Items]
Carrying Value	9,394	9,659
Unfunded Balance	$ 2,085	$ 2,085
Percentage investment held by the entity	15.37%	15.37%
Bank Loans Public and Private Corporate Bonds Asset Backed Securities Equity and Debt Restructuring [Member]
Investment Securities [Line Items]
Carrying Value	$ 5,691	$ 5,985
Percentage investment held by the entity	1.76%	1.76%
Power Utility and Energy Industries and Infrastructure [Member]
Investment Securities [Line Items]
Carrying Value	$ 6,289	$ 9,188
Unfunded Balance	$ 1,401	$ 1,391
Percentage investment held by the entity	0.18%	0.18%
Senior and Junior Debts of Private Equity-Backed Companies [Member]
Investment Securities [Line Items]
Carrying Value	$ 3,071	$ 1,602
Unfunded Balance	$ 1,542	$ 3,106
Percentage investment held by the entity	0.47%	0.47%
Mature Real Estate Private Equity Funds And Portfolio Globally [Member]
Investment Securities [Line Items]
Carrying Value	$ 1,732	$ 1,912
Unfunded Balance	$ 8,632	$ 8,548
Percentage investment held by the entity	2.24%	2.24%