Financial Highlights Per Share Performance - Summary of per share data (Detail) - $ / shares	3 Months Ended		9 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Investment Company, Financial Highlights [Roll Forward]
Net asset value, beginning of period	$ 4.42	$ 4.76	$ 6.43	$ 0.54
Net (decrease) increase in net assets from investment operations:
Net investment loss	(0.01)	(0.06)	(0.09)	(0.09)
Net realized and unrealized (loss) gain	(3.26)	1.33	(5.19)	5.58
Net (decrease) increase in net assets resulting from operations	(3.27)	1.27	(5.28)	5.49
Net asset value, end of period	$ 1.15	$ 6.03	$ 1.15	$ 6.03
Total return	(73.98%)	26.68%	(82.12%)	1016.67%
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%)