Financial Highlights Per Share Performance - Summary of Per Share Data (Detail) - $ / shares	3 Months Ended		6 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Mar. 31, 2024	Mar. 31, 2023
Investment Company, Financial Highlights [Roll Forward]
Principal market net asset value, beginning of period	$ 0.8	$ 0.82	$ 0.68	$ 1.27
Net increase (decrease) in net assets from investment operations:
Net investment loss	(0.01)	(0.01)	(0.01)	(0.01)
Net realized and unrealized gain (loss)	0.5	0.17	0.62	(0.28)
Net increase (decrease) in net assets resulting from operations	0.49	0.16	0.61	(0.29)
Principal market net asset value, end of period	$ 1.29	$ 0.98	$ 1.29	$ 0.98
Total return	61.25%	19.51%	89.71%	(22.83%)
Ratios to average net assets:
Net investment loss	(2.50%)	(2.50%)	(2.50%)	(2.50%)
Expenses	(2.50%)	(2.50%)	(2.50%)	(2.50%)