Note 2 - Significant Accounting Policies - Activity in Silver Bullion (Details) $ in Thousands	3 Months Ended			6 Months Ended			12 Months Ended
	Jun. 30, 2016 USD ($) oz		Jun. 30, 2015 USD ($) oz	Jun. 30, 2016 USD ($) oz		Jun. 30, 2015 USD ($) oz	Dec. 31, 2015 USD ($) oz
Beginning balance (in Ounces) | oz	332,578,500		321,975,600	317,934,900		329,564,200	329,564,200
Beginning balance, average cost	$ 6,159,729		$ 6,212,172	$ 5,979,252		$ 6,386,750	$ 6,386,750
Beginning balance, fair value	$ 5,115,057		$ 5,344,795	$ 4,393,861	[1]	$ 5,263,140	5,263,140
Silver bullion contributed (in Ounces) | oz	20,970,000		24,658,400	47,957,100		35,425,500
Silver bullion contributed, average cost	$ 349,869		$ 398,520	$ 762,070		$ 579,038
Silver bullion contributed, fair value	$ 349,869		$ 398,520	$ 762,070		$ 579,038
Silver bullion distributed (in Ounces) | oz	(19,587,600)		(20,883,000)	(31,540,200)		(38,829,500)
Silver bullion distributed, average cost	$ (361,122)		$ (385,063)	$ (585,504)		$ (732,243)
Silver bullion distributed, fair value	(337,120)		(341,336)	(510,105)		(646,475)
Silver bullion distributed, realized gain (loss)	$ (24,002)		$ (43,727)	$ (75,399)		$ (85,768)
Silver bullion sold to pay expenses (in Ounces) | oz	(416,000)		(408,400)	(806,900)		(817,600)
Silver bullion sold to pay expenses, average cost	$ (7,683)		$ (7,861)	$ (15,025)		$ (15,777)
Silver bullion sold to pay expenses, fair value	(6,751)		(6,718)	(12,390)		(13,465)
Silver bullion sold to pay expenses, realized gain (loss)	(932)		(1,143)	(2,635)		(2,312)
Net realized loss	(24,934)		(44,870)	(78,034)		(88,080)	(212,156)
Net change in unrealized appreciation/depreciation	$ 1,027,763		$ (242,511)	$ 1,568,482		$ 13,722	$ (461,781)
Ending balance (in Ounces) | oz	333,544,900		325,342,600	333,544,900		325,342,600	317,934,900
Ending balance, average cost	$ 6,140,793		$ 6,217,768	$ 6,140,793		$ 6,217,768	$ 5,979,252
Ending balance, fair value	6,123,884	[1]	5,107,880	6,123,884	[1]	5,107,880	4,393,861	[1]
Ending balance, realized gain (loss)	$ (24,934)		$ (44,870)	$ (78,034)		$ (88,080)	$ (212,156)

[1] Cost of investment in silver bullion: $6,140,793 and $5,979,252, respectively.