Note 2 - Significant Accounting Policies - Activity in Silver Bullion (Details)	3 Months Ended						6 Months Ended
	Jun. 30, 2019 USD ($) oz		Mar. 31, 2019 USD ($) oz		Jun. 30, 2018 USD ($) oz	Mar. 31, 2018 USD ($) oz	Jun. 30, 2019 USD ($) oz		Jun. 30, 2018 USD ($) oz
Beginning balance (Ounce) | oz	309,301,232		317,233,610		319,012,097	320,629,662	317,233,610		320,629,662
Silver bullion contributed (Ounce) | oz	20,139,972				24,760,653		32,006,044		35,696,104
Silver bullion distributed (Ounce) | oz	(5,715,084)				(20,901,664)		(25,136,052)		(33,066,784)
Silver bullion sold to pay expenses (Ounce) | oz	(395,507)				(405,372)		(772,989)		(793,268)
Ending balance (Ounce) | oz	323,330,613		309,301,232		322,465,714	319,012,097	323,330,613		322,465,714
Beginning balance, average cost	$ 5,475,186,353		$ 5,641,558,156		$ 5,786,442,301	$ 5,831,748,196	$ 5,641,558,156		$ 5,831,748,196
Silver bullion contributed, average cost	300,557,309				404,809,725		485,837,021		587,710,858
Silver bullion distributed, average cost	(100,797,226)				(377,908,569)		(445,746,844)		(599,066,227)
Silver bullion sold to pay expenses, average cost	(6,983,443)				(7,335,219)		(13,685,340)		(14,384,589)
Ending balance, average cost	5,667,962,993		5,475,186,353		5,806,008,238	5,786,442,301	5,667,962,993		5,806,008,238
Beginning balance, fair value	4,670,448,601		4,906,017,787	[1]	5,193,516,929	5,407,419,250	4,906,017,787	[1]	5,407,419,250
Silver bullion contributed, fair value	300,557,309				404,809,725		485,837,021		587,710,858
Silver bullion distributed, fair value	(84,431,118)				(350,390,495)		(387,112,201)		(557,768,350)
Silver bullion sold to pay expenses, fair value	(5,887,355)				(6,646,976)		(11,803,469)		(13,189,884)
Net realized gain (loss), fair value	(17,462,196)		(43,054,318)		(28,206,317)	(14,286,265)	(60,516,514)		(42,492,582)
Net change in unrealized appreciation/depreciation, fair value	57,866,685		(69,197,383)		(43,957,463)	(168,596,426)	(11,330,698)		(212,553,889)
Ending balance, fair value	4,921,091,926	[1]	4,670,448,601		5,169,125,403	5,193,516,929	4,921,091,926	[1]	5,169,125,403
Silver bullion distributed, realized gain (loss)	(16,366,108)				(27,518,074)		(58,634,643)		(41,297,877)
Silver bullion sold to pay expenses, realized gain (loss)	(1,096,088)				(688,243)		(1,881,871)		(1,194,705)
Ending balance, realized gain (loss)	$ (17,462,196)		$ (43,054,318)		$ (28,206,317)	$ (14,286,265)	$ (60,516,514)		$ (42,492,582)

[1] Cost of investment in silver bullion: $5,667,962,993 and $5,641,558,156, respectively.