Note 2 - Significant Accounting Policies - Activity in Silver Bullion (Details)	12 Months Ended
	Dec. 31, 2018 USD ($) oz		Dec. 31, 2017 USD ($) oz		Dec. 31, 2016 USD ($) oz
Beginning balance (Ounce) | oz	320,629,662		341,348,242		317,934,907
Silver bullion contributed (Ounce) | oz	60,236,118		52,760,584		97,670,323
Silver bullion distributed (Ounce) | oz	(62,004,144)		(71,810,555)		(72,574,751)
Silver bullion sold to pay expenses (Ounce) | oz	(1,628,026)		(1,668,609)		(1,682,237)
Ending balance (Ounce) | oz	317,233,610		320,629,662		341,348,242
Beginning balance, average cost	$ 5,831,748,196		$ 6,305,715,839		$ 5,979,251,955
Silver bullion contributed, average cost	954,051,929		873,170,446		1,702,628,324
Silver bullion distributed, average cost	(1,114,932,000)		(1,316,488,192)		(1,344,950,576)
Silver bullion sold to pay expenses, average cost	(29,309,969)		(30,649,897)		(31,213,864)
Ending balance, average cost	5,641,558,156		5,831,748,196		6,305,715,839
Beginning balance, fair value	5,407,419,250	[1]	5,543,495,441		4,393,860,514
Silver bullion contributed, fair value	954,051,929		873,170,446		1,702,628,324
Silver bullion distributed, fair value	(982,882,736)		(1,226,578,286)		(1,236,224,053)
Silver bullion sold to pay expenses, fair value	(25,579,758)		(28,438,986)		(28,700,680)
Net realized gain (loss), fair value	(135,779,475)		(92,120,817)		(111,239,707)
Net change in unrealized appreciation/depreciation, fair value	(311,211,423)		337,891,452		823,171,043
Ending balance, fair value	4,906,017,787	[1]	5,407,419,250	[1]	5,543,495,441
Silver bullion distributed, realized gain (loss)	(132,049,264)		(89,909,906)		(108,726,523)
Silver bullion sold to pay expenses, realized gain (loss)	(3,730,211)		(2,210,911)		(2,513,184)
Ending balance, realized gain (loss)	$ (135,779,475)		$ (92,120,817)		$ (111,239,707)

[1] Cost of investment in silver bullion: $5,641,558,156 and $5,831,748,196, respectively.