Note 2 - Significant Accounting Policies - Activity in Silver Bullion (Details)	12 Months Ended
	Dec. 31, 2019 USD ($) oz		Dec. 31, 2018 USD ($) oz		Dec. 31, 2017 USD ($) oz
Beginning balance (Ounce) | oz	317,233,610		320,629,662		341,348,242
Beginning balance, average cost	$ 5,641,558,156		$ 5,831,748,196		$ 6,305,715,839
Beginning balance, fair value	$ 4,906,017,787	[1]	$ 5,407,419,250		$ 5,543,495,441
Silver bullion contributed (Ounce) | oz	113,045,188		60,236,118		52,760,584
Silver bullion contributed, average cost	$ 1,836,353,140		$ 954,051,929		$ 873,170,446
Silver bullion contributed, fair value	$ 1,836,353,140		$ 954,051,929		$ 873,170,446
Silver bullion distributed (Ounce) | oz	(65,991,660)		(62,004,144)		(71,810,555)
Silver bullion distributed, average cost	$ (1,154,479,083)		$ (1,114,932,000)		$ (1,316,488,192)
Silver bullion distributed, fair value	(1,101,564,648)		(982,882,736)		(1,226,578,286)
Silver bullion distributed, realized gain (loss)	$ (52,914,435)		$ (132,049,264)		$ (89,909,906)
Silver bullion sold to pay expenses (Ounce) | oz	(1,670,427)		(1,628,026)		(1,668,609)
Silver bullion sold to pay expenses, average cost	$ (29,275,167)		$ (29,309,969)		$ (30,649,897)
Silver bullion sold to pay expenses, fair value	(27,086,721)		(25,579,758)		(28,438,986)
Silver bullion sold to pay expenses, realized gain (loss)	(2,188,446)		(3,730,211)		(2,210,911)
Net realized gain (loss), fair value	(55,102,881)		(135,779,475)		(92,120,817)
Net change in unrealized appreciation/depreciation, fair value	$ 984,801,878		$ (311,211,423)		$ 337,891,452
Ending balance (Ounce) | oz	362,616,711		317,233,610		320,629,662
Ending balance, average cost	$ 6,294,157,046		$ 5,641,558,156		$ 5,831,748,196
Ending balance, fair value	6,543,418,555	[1]	4,906,017,787	[1]	5,407,419,250
Ending balance, realized gain (loss)	$ (55,102,881)		$ (135,779,475)		$ (92,120,817)

[1] Cost of investment in silver bullion: $6,294,157,046 and $5,641,558,156, respectively.