Statements of Changes in Net Assets - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Net Assets, Beginning of Year	$ 10,147,507,137	$ 7,310,131,020	$ 5,209,802,846
Operations:
Net investment loss	(27,533,111)	(21,630,631)	(20,312,154)
Net realized gain	23,491,426	22,215,914	25,068,804
Net change in unrealized appreciation/depreciation	(194,080,795)	881,278,079	303,987,270
Net increase (decrease) in net assets resulting from operations	(198,122,480)	881,863,362	308,743,920
Capital Share Transactions:
Contributions for Shares issued	3,078,649,161	2,782,113,163	3,784,339,342
Distributions for Shares redeemed	(1,483,295,672)	(826,600,408)	(1,992,755,088)
Net increase in net assets from capital share transactions	1,595,353,489	1,955,512,755	1,791,584,254
Increase in net assets	1,397,231,009	2,837,376,117	2,100,328,174
Net Assets, End of Year	$ 11,544,738,146	$ 10,147,507,137	$ 7,310,131,020
Shares issued and redeemed
Shares issued (in shares)	247,000,000	228,250,000	314,850,000
Shares redeemed (in shares)	(121,700,000)	(68,350,000)	(167,950,000)
Net increase in Shares issued and outstanding (in shares)	125,300,000	159,900,000	146,900,000