Note 2 - Significant Accounting Policies - Activity in Silver Bullion (Details)	3 Months Ended
	Mar. 31, 2020 USD ($) oz		Mar. 31, 2019 USD ($) oz
Beginning balance (Ounce) | oz	362,616,711		317,233,610
Beginning balance, average cost	$ 6,294,157,046		$ 5,641,558,156
Beginning balance, fair value	$ 6,543,418,555	[1]	$ 4,906,017,787
Silver bullion contributed (Ounce) | oz	61,719,272		11,866,072
Silver bullion contributed, average cost	$ 889,817,438		$ 185,279,712
Silver bullion contributed, fair value	$ 889,817,438		$ 185,279,712
Silver bullion distributed (Ounce) | oz	(28,512,880)		(19,420,968)
Silver bullion distributed, average cost	$ (494,644,937)		$ (344,949,618)
Silver bullion distributed, fair value	(484,999,588)		(302,681,083)
Silver bullion distributed, realized gain (loss)	$ (9,645,349)		$ (42,268,535)
Silver bullion sold to pay expenses (Ounce) | oz	(454,637)		(377,482)
Silver bullion sold to pay expenses, average cost	$ (7,896,659)		$ (6,701,897)
Silver bullion sold to pay expenses, fair value	(7,971,299)		(5,916,114)
Silver bullion sold to pay expenses, realized gain (loss)	74,640		(785,783)
Net realized gain (loss), fair value	(9,570,709)		(43,054,318)
Net change in unrealized appreciation/depreciation, fair value	$ (1,423,211,664)		$ (69,197,383)
Ending balance (Ounce) | oz	395,368,466		309,301,232
Ending balance, average cost	$ 6,681,432,888		$ 5,475,186,353
Ending balance, fair value	5,507,482,733	[1]	4,670,448,601
Ending balance, realized gain (loss)	$ (9,570,709)		$ (43,054,318)

[1] Cost of investment in silver bullion: $6,681,432,888 and $6,294,157,046, respectively.