Note 2 - Significant Accounting Policies - Share Activity (Details) - USD ($)		12 Months Ended
		Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Shares issued (in shares)	[1]	53,075,000	359,650,000	191,675,000
Shares issued, amount	[1]	$ 1,853,104,516	$ 12,103,493,289	$ 5,226,042,788
Shares redeemed (in shares)	[1]	(108,550,000)	(80,000,000)	(56,200,000)
Distributions for Shares redeemed	[1]	$ (3,649,216,540)	$ (2,617,761,048)	$ (1,418,257,979)
Net increase (decrease) in Shares issued and outstanding (in shares)		(55,475,000)	279,650,000	135,475,000
Net increase (decrease) in net assets from capital share transactions		$ (1,796,112,024)	$ 9,485,732,241	$ 3,807,784,809

[1] Share transactions reflect a one-for-two reverse stock split effective at market open on May 24, 2021.