Note 2 - Significant Accounting Policies - Activity in Silver Bullion (Details)	3 Months Ended
	Mar. 31, 2021 USD ($) oz		Mar. 31, 2020 USD ($) oz
Beginning balance (Ounce) | oz	558,715,882		362,616,711
Beginning balance, average cost	$ 10,472,474,303		$ 6,294,157,046
Beginning balance, fair value	$ 14,797,590,146	[1]	$ 6,543,418,555
Silver bullion contributed (Ounce) | oz	164,157,109		61,719,272
Silver bullion contributed, average cost	$ 4,468,670,836		$ 889,817,438
Silver bullion contributed, fair value	$ 4,468,670,836		$ 889,817,438
Silver bullion distributed (Ounce) | oz	(147,079,936)		(28,512,880)
Silver bullion distributed, average cost	$ (2,990,074,263)		$ (494,644,937)
Silver bullion distributed, fair value	(3,878,623,508)		(484,999,588)
Silver bullion distributed, realized gain (loss)	$ 888,549,245		$ (9,645,349)
Silver bullion sold to pay expenses (Ounce) | oz	(668,843)		(454,637)
Silver bullion sold to pay expenses, average cost	$ (13,426,100)		$ (7,896,659)
Silver bullion sold to pay expenses, fair value	(18,635,427)		(7,971,299)
Silver bullion sold to pay expenses, realized gain (loss)	5,209,327		74,640
Net realized gain (loss), fair value	893,758,572		(9,570,709)
Net change in unrealized appreciation/depreciation, fair value	$ (2,459,779,533)		$ (1,423,211,664)
Ending balance (Ounce) | oz	575,124,212		395,368,466
Ending balance, average cost	$ 11,937,644,776		$ 6,681,432,888
Ending balance, fair value	13,802,981,086	[1]	5,507,482,733
Ending balance, realized gain (loss)	$ 893,758,572		$ (9,570,709)

[1] Cost of investment in silver bullion: $11,937,644,776 and $10,472,474,303, respectively.