Statements of Changes in Net Assets - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Net Assets, Beginning of Year	$ 1,209,866,609	$ 1,393,408,765	$ 1,035,799,565
Operations:
Net investment income (loss)	13,025,842	12,572,317	(160,492)
Net realized gain (loss)	25,714,301	(11,936,763)	3,413,696
Net change in unrealized appreciation/depreciation	136,196,816	(190,844,004)	77,165,412
Net increase (decrease) in net assets resulting from operations	174,936,959	(190,208,450)	80,418,616
Capital Share Transactions:
Contributions for Shares issued	180,290,776	277,791,824	349,609,325
Distributions for Shares redeemed	(789,751,239)	(271,125,530)	(72,418,741)
Net increase (decrease) in net assets from capital share transactions	(609,460,463)	6,666,294	277,190,584
Increase (decrease) in net assets	(434,523,504)	(183,542,156)	357,609,200
Net Assets, End of Year	$ 775,343,105	$ 1,209,866,609	$ 1,393,408,765
Shares issued and redeemed
Shares issued (in shares)	11,950,000	17,100,000	24,050,000
Shares redeemed (in shares)	(50,700,000)	(16,000,000)	(4,950,000)
Net increase (decrease) in Shares issued and outstanding (in shares)	(38,750,000)	1,100,000	19,100,000