CONSOLIDATED STATEMENTS OF CHANGES IN SHAREHOLDERS' EQUITY - USD ($) $ in Thousands	Common Stock and Additional Paid-in Capital Lexam VG Gold	Common Stock and Additional Paid-in Capital Registered direct offering	Common Stock and Additional Paid-in Capital	Accumulated Other Comprehensive (Loss) Income	Accumulated Deficit	Lexam VG Gold	Black Fox	Registered direct offering	Total
Balance at Dec. 31, 2016			$ 1,360,345	$ 1,666	$ (918,972)				$ 443,039
Balance (in shares) at Dec. 31, 2016			299,570,000
Increase (Decrease) in Shareholders' Equity
Stock-based compensation			$ 1,311						1,311
Shares issued in connection with acquisitions	$ 38,141					$ 38,141
Shares issued in connection with acquisitions (in shares)	12,687,000
Stock issued during the period			$ 43,220						43,220
Stock issued during the period (in shares)			20,700,000
Exercise of stock options			$ 122						$ 122
Exercise of stock options (in shares)			94,000						94,000
Shareholder distributions			$ (3,059)						$ (3,059)
Other-than-temporary impairment on marketable equity securities				356					356
Reclassification of unrealized gain on marketable securities disposed of during the period, net of taxes				(840)					(840)
Unrealized gain on available-for-sale securities, net of taxes				1,818					1,818
Net loss					(10,634)				(10,634)
Balance at Dec. 31, 2017			$ 1,447,879	3,000	(929,606)				521,273
Balance (in shares) at Dec. 31, 2017			337,051,000
Increase (Decrease) in Shareholders' Equity
Adoption of ASU 2016-01 (note 2) | Accounting Standards Update 2016-01				$ (3,000)	3,000
Balance			$ 1,447,879		(926,606)				521,273
Stock-based compensation			269						269
Shares issued in connection with acquisitions (in shares)							178,321
Stock issued during the period			$ 918						918
Stock issued during the period (in shares)			515,000
Exercise of stock options			$ 192						$ 192
Exercise of stock options (in shares)			182,000						171,000
Shareholder distributions			$ (3,372)						$ (3,372)
Shares issued for acquisition of mineral property interests			$ 391						391
Shares issued for acquisition of mineral property interests (in shares)			178,000
Net loss					(44,870)				(44,870)
Balance at Dec. 31, 2018			$ 1,457,422		(971,476)				485,946
Balance (in shares) at Dec. 31, 2018			344,560,000
Increase (Decrease) in Shareholders' Equity
Stock-based compensation			$ 694						694
Stock issued during the period		$ 69,467	$ 1,851					$ 69,467	1,851
Stock issued during the period (in shares)		53,880,000	1,010,000
Exercise of stock options			$ 544						$ 544
Exercise of stock options (in shares)			535,000						535,000
Shares issued for acquisition of mineral property interests			$ 724						$ 724
Shares issued for acquisition of mineral property interests (in shares)			354,000
Net loss					(59,747)				(59,747)
Balance at Dec. 31, 2019			$ 1,530,702		$ (1,031,223)				$ 499,479
Balance (in shares) at Dec. 31, 2019			400,339,000