Fair Value of Financial Instruments - Additional Information (Detail) - USD ($)	Dec. 31, 2019	Dec. 31, 2018
Fair Value Disclosures [Abstract]
Investments, at fair value	$ 144,195,000	$ 82,500,000

Value of the investment at close of period. For schedules of investments that are categorized, the value would be aggregated by category. For investment in and advances to affiliates, if operations of any controlled companies are different in character from those of the company, group such affiliates within divisions and by type of activities.

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Name:	us-gaap_InvestmentOwnedAtFairValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant