FINANCIAL HIGHLIGHTS (Details) - $ / shares		3 Months Ended		9 Months Ended
		Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Per Share Operating Performance:
Net asset value, beginning of period		$ 35.86	$ 18.89	$ 24.29	$ 32.31
Total income (loss)		2.68	1.18	14.38	(12.18)
Total expenses		(0.09)	(0.04)	(0.22)	(0.10)
Net increase (decrease) in net asset value		2.59	1.14	14.16	(12.28)
Net asset value, end of period		$ 38.45	$ 20.03	$ 38.45	$ 20.03
Total Return		7.22%	6.03%	58.30%	(38.01%)
Ratios to Average Net Assets
Total income (loss)		5.46%	6.75%	43.03%	40.10%
Management fees	[1]	0.60%	0.60%	0.60%	0.60%
Total expenses excluding management fees	[1]	0.38%	0.37%	0.36%	0.42%
Expense waived	[1]	0.00%	(0.22%)	(0.08%)	(0.27%)
Net expense excluding management fees	[1]	0.38%	0.15%	0.28%	0.15%
Net income (loss)		5.21%	6.56%	42.37%	39.54%

[1] Annualized.