Note 2 - Significant Accounting Policies - Activity in Silver Bullion (Details)	3 Months Ended						6 Months Ended
	Jun. 30, 2021 USD ($) oz		Mar. 31, 2021 USD ($) oz		Jun. 30, 2020 USD ($) oz	Mar. 31, 2020 USD ($) oz	Jun. 30, 2021 USD ($) oz		Jun. 30, 2020 USD ($) oz
Beginning balance (Ounce) | oz	575,124,212		558,715,882		395,368,466	362,616,711	558,715,882		362,616,711
Beginning balance, average cost	$ 11,937,644,776		$ 10,472,474,303		$ 6,681,432,888	$ 6,294,157,046	$ 10,472,474,303		$ 6,294,157,046
Beginning balance, fair value	$ 13,802,981,086		14,797,590,146	[1]	$ 5,507,482,733	6,543,418,555	$ 14,797,590,146	[1]	$ 6,543,418,555
Silver bullion contributed (Ounce) | oz	28,106,701				118,708,634		192,263,810		180,427,906
Silver bullion contributed, average cost	$ 765,794,167				$ 1,962,530,775		$ 5,234,465,003		$ 2,852,348,213
Silver bullion contributed, fair value	$ 765,794,167				$ 1,962,530,775		$ 5,234,465,003		$ 2,852,348,213
Silver bullion distributed (Ounce) | oz	(44,335,250)				(15,569,065)		(191,415,186)		(44,081,945)
Silver bullion distributed, average cost	$ (928,983,617)				$ (261,348,495)		$ (3,919,057,880)		$ (755,993,432)
Silver bullion distributed, fair value	(1,177,999,610)				(250,788,865)		(5,056,623,118)		(735,788,453)
Silver bullion distributed, realized gain (loss)	$ 249,015,993				$ (10,559,630)		$ 1,137,565,238		$ (20,204,979)
Silver bullion sold to pay expenses (Ounce) | oz	(722,380)				(500,537)		(1,391,223)		(955,174)
Silver bullion sold to pay expenses, average cost	$ (15,051,815)				$ (8,415,355)		$ (28,477,915)		$ (16,312,014)
Silver bullion sold to pay expenses, fair value	(19,036,249)				(7,832,116)		(37,671,676)		(15,803,415)
Silver bullion sold to pay expenses, realized gain (loss)	3,984,434				(583,239)		9,193,761		(508,599)
Net realized gain (loss), fair value	253,000,427		893,758,572		(11,142,869)	(9,570,709)	1,146,758,999		(20,713,578)
Net change in unrealized appreciation/depreciation, fair value	$ 756,594,817		$ (2,459,779,533)		$ 1,686,694,147	$ (1,423,211,664)	$ (1,703,184,716)		$ 263,482,483
Ending balance (Ounce) | oz	558,173,283		575,124,212		498,007,498	395,368,466	558,173,283		498,007,498
Ending balance, average cost	$ 11,759,403,511		$ 11,937,644,776		$ 8,374,199,813	$ 6,681,432,888	$ 11,759,403,511		$ 8,374,199,813
Ending balance, fair value	14,381,334,638	[1]	13,802,981,086		8,886,943,805	5,507,482,733	14,381,334,638	[1]	8,886,943,805
Ending balance, realized gain (loss)	$ 253,000,427		$ 893,758,572		$ (11,142,869)	$ (9,570,709)	$ 1,146,758,999		$ (20,713,578)

[1] Cost of investment in silver bullion: $11,759,403,511 and $10,472,474,303, respectively.