Net Asset Value and Financial Highlights - Schedule of Net Asset Value and Financial Highlights (Parenthetical) (Detail) - Maximum [Member] - $ / shares	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Investment Company, Financial Highlights [Line Items]
Brokerage fees/commissions, per share	$ 0.02	$ 0.02	$ 0.02
Investment Company, Investment Income (Loss), Per Share	$ 0.01

Per share or unit amount, after investment expense, of dividend and interest investment income (loss).

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 946
-SubTopic 205
-Section 50
-Paragraph 7
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=25866437&loc=d3e10246-115837

Name:	us-gaap_InvestmentCompanyInvestmentIncomeLossPerShare
Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	duration