Note 2 - Significant Accounting Policies - Activity in Silver Bullion (Details)	3 Months Ended			12 Months Ended
	Mar. 31, 2017 USD ($) oz		Mar. 31, 2016 USD ($) oz	Dec. 31, 2016 USD ($) oz
Beginning balance (Ounce) | oz	341,348,242		317,934,907	317,934,907
Beginning balance, average cost	$ 6,305,715,839		$ 5,979,251,955	$ 5,979,251,955
Beginning balance, fair value	$ 5,543,495,441	[1]	$ 4,393,860,514	4,393,860,514
Silver bullion contributed (Ounce) | oz	4,830,754		26,987,106
Silver bullion contributed, average cost	$ 84,171,380		$ 412,201,487
Silver bullion contributed, fair value	$ 84,171,380		$ 412,201,487
Silver bullion distributed (Ounce) | oz	(15,443,140)		(11,952,590)
Silver bullion distributed, average cost	$ (285,204,911)		$ (224,382,205)
Silver bullion distributed, fair value	(269,671,252)		(172,985,000)
Silver bullion distributed, realized gain (loss)	$ (15,533,659)		$ (51,397,205)
Silver bullion sold to pay expenses (Ounce) | oz	(409,659)		(390,915)
Silver bullion sold to pay expenses, average cost	$ (7,566,576)		$ (7,341,829)
Silver bullion sold to pay expenses, fair value	(7,056,499)		(5,638,637)
Silver bullion sold to pay expenses, realized gain (loss)	(510,077)		(1,703,192)
Net realized gain (loss), fair value	(16,043,736)		(53,100,397)	(111,239,707)
Net change in unrealized appreciation/depreciation, fair value	$ 630,795,770		$ 540,719,490	$ 823,171,043
Ending balance (Ounce) | oz	330,326,197		332,578,508	341,348,242
Ending balance, average cost	$ 6,097,115,732		$ 6,159,729,408	$ 6,305,715,839
Ending balance, fair value	5,965,691,104	[1]	5,115,057,457	5,543,495,441	[1]
Ending balance, realized gain (loss)	$ (16,043,736)		$ (53,100,397)	$ (111,239,707)

[1] Cost of investment in silver bullion: $6,097,115,732 and $6,305,715,839, respectively.