Investments (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Available-for-sale Securities [Abstract]
Gain (Loss) on Investments	$ 4,529	$ (1,471)
Marketable Securities, Realized Gain (Loss)	313	1,471
Marketable Securities, Unrealized Gain (Loss)	4,842	$ 0
Investment in Marketable Securities (Textual) [Abstract]
Held-to-maturity Securities, Restricted	22,100		$ 17,600
Equity securities
Available-for-sale Securities
Cost	19,686		21,771
Available-for-sale Debt Securities, Accumulated Gross Unrealized Loss, before Tax	(1,478)		(881)
Available-for-sale Equity Securities, Accumulated Gross Unrealized Gain, before Tax	12,795		7,355
Available-for-sale Securities	31,003		28,245
Debt Securities
Available-for-sale Securities
Available-for-sale Debt Securities, Accumulated Gross Unrealized Loss, before Tax			(363)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss			363
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value			6,314
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value			0
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value			6,314
Equity and debt securities
Available-for-sale Securities
Cost	26,363		28,448
Available-for-sale Debt Securities, Accumulated Gross Unrealized Loss, before Tax	(1,841)		(966)
Available-for-sale Equity Securities, Accumulated Gross Unrealized Gain, before Tax	12,795		7,355
Available-for-sale Securities	37,317		34,837
Metalla Royalty & Streaming Ltd. | Equity securities
Available-for-sale Securities
Cost	6,294		6,294
Available-for-sale Debt Securities, Accumulated Gross Unrealized Loss, before Tax	0		0
Available-for-sale Equity Securities, Accumulated Gross Unrealized Gain, before Tax	2,837		1,354
Available-for-sale Securities	9,131		7,648
Metalla Royalty & Streaming Ltd. | Debt Securities
Available-for-sale Securities
Cost	6,677		6,677
Available-for-sale Debt Securities, Accumulated Gross Unrealized Loss, before Tax	(363)		(85)
Available-for-sale Equity Securities, Accumulated Gross Unrealized Gain, before Tax	0		0
Available-for-sale Securities			6,592
Corvus Gold Inc. [Member] | Equity securities
Available-for-sale Securities
Cost	3,582		3,582
Available-for-sale Debt Securities, Accumulated Gross Unrealized Loss, before Tax	0		0
Available-for-sale Equity Securities, Accumulated Gross Unrealized Gain, before Tax	6,844		4,518
Available-for-sale Securities	10,426		8,100
Almaden Minerals, Ltd. [Member] | Equity securities
Available-for-sale Securities
Cost	2,067		3,125
Available-for-sale Debt Securities, Accumulated Gross Unrealized Loss, before Tax	(727)		(235)
Available-for-sale Equity Securities, Accumulated Gross Unrealized Gain, before Tax	0		0
Available-for-sale Securities	1,340		2,890
Northern Empire Resources Corp. [Member] | Equity securities
Available-for-sale Securities
Cost	4,489		4,489
Available-for-sale Debt Securities, Accumulated Gross Unrealized Loss, before Tax	0		0
Available-for-sale Equity Securities, Accumulated Gross Unrealized Gain, before Tax	2,999		1,077
Available-for-sale Securities	7,488		5,566
Rockhaven Resources, Ltd. [Member] | Equity securities
Available-for-sale Securities
Cost	2,064		2,064
Available-for-sale Debt Securities, Accumulated Gross Unrealized Loss, before Tax	(596)		(193)
Available-for-sale Equity Securities, Accumulated Gross Unrealized Gain, before Tax	0		0
Available-for-sale Securities	1,468		1,871
Other Investments [Member] | Equity securities
Available-for-sale Securities
Cost	1,190		1,479
Available-for-sale Debt Securities, Accumulated Gross Unrealized Loss, before Tax	(155)		(453)
Available-for-sale Equity Securities, Accumulated Gross Unrealized Gain, before Tax	115		405
Available-for-sale Securities	1,150		1,431
Kootenay Silver, Inc. [Member] | Equity securities
Available-for-sale Securities
Cost			738
Available-for-sale Debt Securities, Accumulated Gross Unrealized Loss, before Tax			0
Available-for-sale Equity Securities, Accumulated Gross Unrealized Gain, before Tax			1
Available-for-sale Securities			739
Level 3 | Equity and debt securities
Available-for-sale Securities
Available-for-sale Securities			$ 6,891
Available-for-sale Securities | Level 3 | Equity and debt securities
Available-for-sale Securities
Available-for-sale Securities	$ 6,314