CONSOLIDATED STATEMENTS OF CHANGES IN SHAREHOLDERS' EQUITY - USD ($) $ in Thousands	Common Stock Registered direct offering	Common Stock ATM offering	Common Stock	Warrants	Accumulated Deficit	Registered direct offering	ATM offering	Total
Balance (in shares) at Dec. 31, 2017			337,051,000
Balance at Dec. 31, 2017			$ 1,447,879		$ (926,606)			$ 521,273
Increase (Decrease) in Shareholders' Equity
Stock-based compensation			182					182
Exercise of stock options			$ 63					$ 63
Exercise of stock options (in shares)			57,000					57,199
Shareholder distribution			$ (3,373)					$ (3,373)
Shares issued for acquisition of mineral property interests			$ 391					391
Shares issued for acquisition of mineral property interests (in shares)			178,000
Net income (loss)					(23,881)			(23,881)
Balance at Sep. 30, 2018			$ 1,445,142		(950,487)			494,655
Balance (in shares) at Sep. 30, 2018			337,286,000
Balance at Jun. 30, 2018			$ 1,447,025		(937,197)			509,828
Balance (in shares) at Jun. 30, 2018			337,268,000
Increase (Decrease) in Shareholders' Equity
Stock-based compensation			$ (214)					(214)
Exercise of stock options			$ 18					18
Exercise of stock options (in shares)			18,000
Shareholder distribution			$ (1,687)					(1,687)
Net income (loss)					(13,290)			(13,290)
Balance at Sep. 30, 2018			$ 1,445,142		(950,487)			494,655
Balance (in shares) at Sep. 30, 2018			337,286,000
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			$ 481					481
Stock issued during the period	$ 22,910	$ 1,851	20,300	$ 2,600		$ 22,910	$ 1,851	22,900
Stock issued during the period (in shares)	16,129,000	1,010,000
Exercise of stock options			$ 411					$ 411
Exercise of stock options (in shares)			405,000					405,000
Shares issued for acquisition of mineral property interests			$ 724					$ 724
Shares issued for acquisition of mineral property interests (in shares)			354,000
Net income (loss)					(34,615)			(34,615)
Balance at Sep. 30, 2019			$ 1,483,799		(1,006,091)			477,708
Balance (in shares) at Sep. 30, 2019			362,458,000
Balance at Jun. 30, 2019			$ 1,482,640		(994,626)			488,014
Balance (in shares) at Jun. 30, 2019			361,957,000
Increase (Decrease) in Shareholders' Equity
Stock-based compensation			$ 284					284
Exercise of stock options			$ 151					151
Exercise of stock options (in shares)			147,000
Shares issued for acquisition of mineral property interests			$ 724					724
Shares issued for acquisition of mineral property interests (in shares)			354,000
Net income (loss)					(11,465)			(11,465)
Balance at Sep. 30, 2019			$ 1,483,799		$ (1,006,091)			$ 477,708
Balance (in shares) at Sep. 30, 2019			362,458,000