Note 2 - Significant Accounting Policies - Activity in Silver Bullion (Details)	3 Months Ended						6 Months Ended
	Jun. 30, 2020 USD ($) oz		Mar. 31, 2020 USD ($) oz		Jun. 30, 2019 USD ($) oz	Mar. 31, 2019 USD ($) oz	Jun. 30, 2020 USD ($) oz		Jun. 30, 2019 USD ($) oz
Beginning balance (Ounce) | oz	395,368,466		362,616,711		309,301,232	317,233,610	362,616,711		317,233,610
Beginning balance, average cost	$ 6,681,432,888		$ 6,294,157,046		$ 5,475,186,353	$ 5,641,558,156	$ 6,294,157,046		$ 5,641,558,156
Beginning balance, fair value	$ 5,507,482,733		6,543,418,555	[1]	$ 4,670,448,601	4,906,017,787	$ 6,543,418,555	[1]	$ 4,906,017,787
Silver bullion contributed (Ounce) | oz	118,708,634				20,139,972		180,427,906		32,006,044
Silver bullion contributed, average cost	$ 1,962,530,775				$ 300,557,309		$ 2,852,348,213		$ 485,837,021
Silver bullion contributed, fair value	$ 1,962,530,775				$ 300,557,309		$ 2,852,348,213		$ 485,837,021
Silver bullion distributed (Ounce) | oz	(15,569,065)				(5,715,084)		(44,081,945)		(25,136,052)
Silver bullion distributed, average cost	$ (261,348,495)				$ (100,797,226)		$ (755,993,432)		$ (445,746,844)
Silver bullion distributed, fair value	(250,788,865)				(84,431,118)		(735,788,453)		(387,112,201)
Silver bullion distributed, realized gain (loss)	$ (10,559,630)				$ (16,366,108)		$ (20,204,979)		$ (58,634,643)
Silver bullion sold to pay expenses (Ounce) | oz	(500,537)				(395,507)		(955,174)		(772,989)
Silver bullion sold to pay expenses, average cost	$ (8,415,355)				$ (6,983,443)		$ (16,312,014)		$ (13,685,340)
Silver bullion sold to pay expenses, fair value	(7,832,116)				(5,887,355)		(15,803,415)		(11,803,469)
Silver bullion sold to pay expenses, realized gain (loss)	(583,239)				(1,096,088)		(508,599)		(1,881,871)
Net realized gain (loss), fair value	(11,142,869)		(9,570,709)		(17,462,196)	(43,054,318)	(20,713,578)		(60,516,514)
Net change in unrealized appreciation/depreciation, fair value	$ 1,686,694,147		$ (1,423,211,664)		$ 57,866,685	$ (69,197,383)	$ 263,482,483		$ (11,330,698)
Ending balance (Ounce) | oz	498,007,498		395,368,466		323,330,613	309,301,232	498,007,498		323,330,613
Ending balance, average cost	$ 8,374,199,813		$ 6,681,432,888		$ 5,667,962,993	$ 5,475,186,353	$ 8,374,199,813		$ 5,667,962,993
Ending balance, fair value	8,886,943,805	[1]	5,507,482,733		4,921,091,926	4,670,448,601	8,886,943,805	[1]	4,921,091,926
Ending balance, realized gain (loss)	$ (11,142,869)		$ (9,570,709)		$ (17,462,196)	$ (43,054,318)	$ (20,713,578)		$ (60,516,514)

[1] Cost of investment in silver bullion: $8,374,199,813 and $6,294,157,046, respectively.