CONSOLIDATED STATEMENTS OF CHANGES IN SHAREHOLDERS' EQUITY - USD ($) shares in Thousands, $ in Thousands	Common Stock Lexam VG Gold	Common Stock Black Fox	Common Stock	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit	Lexam VG Gold	Black Fox	Total
Balance at Dec. 31, 2016			$ 1,360,345	$ 1,666	$ (918,972)			$ 443,039
Balance (in shares) at Dec. 31, 2016			299,570
Increase (Decrease) in Shareholders' Equity
Stock-based compensation (note 9)			$ 1,082					1,082
Sale of shares for cash (note 8)			$ 39,397					39,397
Sale of shares for cash (note 8) (in shares)			20,700
Shares issued in connection with the acquisition (note 8)	$ 38,141					$ 38,141
Shares issued in connection with the acquisition (note 8) (in shares)	12,687
Exercise of stock options (note 8)			$ 47					47
Exercise of stock options (note 8) (in shares)			20
Shareholders' distribution (note 8)			$ (3,059)					(3,059)
Other comprehensive income (note 2)				1,582				1,582
Net loss					(12,800)			(12,800)
Balance at Sep. 30, 2017			$ 1,439,776	3,248	(931,772)			511,252
Balance (in shares) at Sep. 30, 2017			332,977
Balance at Dec. 31, 2016			$ 1,360,345	1,666	(918,972)			443,039
Balance (in shares) at Dec. 31, 2016			299,570
Balance at Dec. 31, 2017			$ 1,447,879	3,000	(929,606)			521,273
Balance (in shares) at Dec. 31, 2017			337,051
Balance at Jun. 30, 2017			$ 1,397,780	4,465	(923,700)			478,545
Balance (in shares) at Jun. 30, 2017			312,277
Increase (Decrease) in Shareholders' Equity
Stock-based compensation (note 9)			$ 337					337
Sale of shares for cash (note 8)			$ 39,397					39,397
Sale of shares for cash (note 8) (in shares)			20,700
Shareholders' distribution (note 8)			$ (1,561)					(1,561)
Other comprehensive income (note 2)				(1,217)				(1,217)
Net loss					(8,072)			(8,072)
Balance at Sep. 30, 2017			$ 1,439,776	3,248	(931,772)			511,252
Balance (in shares) at Sep. 30, 2017			332,977
Increase (Decrease) in Shareholders' Equity
Warrants issued in connection with the equity sale (note 8)			$ 3,823					3,823
Adoption of ASU 2016-01 (note 2) | Accounting Standards Update 2016-01				(3,000)	3,000
Balance at Dec. 31, 2017			$ 1,447,879	$ 3,000	(929,606)			521,273
Balance (in shares) at Dec. 31, 2017			337,051
Balance at Dec. 31, 2017			$ 1,447,879		(926,606)			521,273
Increase (Decrease) in Shareholders' Equity
Stock-based compensation (note 9)			182					182
Sale of shares for cash (note 8)								39,400
Shares issued in connection with the acquisition (note 8)		$ 391					$ 391
Shares issued in connection with the acquisition (note 8) (in shares)		178
Exercise of stock options (note 8)			$ 63					63
Exercise of stock options (note 8) (in shares)			57
Shareholders' distribution (note 8)			$ (3,372)					(3,372)
Net loss					(23,881)			(23,881)
Balance at Sep. 30, 2018			$ 1,445,143		(950,487)			494,656
Balance (in shares) at Sep. 30, 2018			337,286
Balance at Jun. 30, 2018			$ 1,447,026		(937,197)			509,829
Balance (in shares) at Jun. 30, 2018			337,268
Increase (Decrease) in Shareholders' Equity
Stock-based compensation (note 9)			$ (214)					(214)
Exercise of stock options (note 8)			$ 18					18
Exercise of stock options (note 8) (in shares)			18
Shareholders' distribution (note 8)			$ (1,687)					(1,687)
Net loss					(13,290)			(13,290)
Balance at Sep. 30, 2018			$ 1,445,143		$ (950,487)			$ 494,656
Balance (in shares) at Sep. 30, 2018			337,286