Statements of Changes in Net Assets - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Net Assets, Beginning of Year	$ 5,209,802,846	$ 6,213,387,199	$ 6,271,029,069
Operations:
Net investment loss	(20,312,154)	(15,245,766)	(16,627,675)
Net realized gain (loss)	25,068,804	(87,792,181)	14,368,742
Net change in unrealized appreciation/depreciation	303,987,270	(659,078,052)	(40,157,712)
Net increase (decrease) in net assets resulting from operations	308,743,920	(762,115,999)	(42,416,645)
Capital Share Transactions:
Contributions for Shares issued	3,784,339,342	830,130,993	590,756,513
Distributions for Shares redeemed	(1,992,755,088)	(1,071,599,347)	(605,981,738)
Net increase (decrease) in net assets from capital share transactions	1,791,584,254	(241,468,354)	(15,225,225)
Increase (decrease) in net assets	2,100,328,174	(1,003,584,353)	(57,641,870)
Net Assets, End of Year	$ 7,310,131,020	$ 5,209,802,846	$ 6,213,387,199
Shares issued and redeemed
Shares issued (in shares)	314,850,000	72,050,000	48,100,000
Shares redeemed (in shares)	(167,950,000)	(99,350,000)	(50,700,000)
Net increase (decrease) in Shares issued and outstanding (in shares)	146,900,000	(27,300,000)	(2,600,000)