Financial Highlights Per Share Performance - Summary of Per Share Data (Detail) - $ / shares	3 Months Ended		9 Months Ended
	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024
Investment Company, Financial Highlights [Roll Forward]
Principal Market NAV, beginning of period	$ 0.75	$ 1.29	$ 0.7	$ 0.68
Net decrease in net assets from investment operations:
Net investment loss	0	0	(0.02)	(0.02)
Net realized and unrealized loss	(0.13)	(0.72)	(0.06)	(0.09)
Net decrease in net assets resulting from operations	(0.13)	(0.72)	(0.08)	(0.11)
Principal Market NAV, end of period	$ 0.62	$ 0.57	$ 0.62	$ 0.57
Total return	(17.33%)	(55.81%)	(11.43%)	(16.18%)
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%)