CONSOLIDATED STATEMENTS OF CHANGES IN SHAREHOLDERS' EQUITY - USD ($) $ in Thousands	Common Stock Direct Offering	Common Stock ATM offering	Common Stock	Warrants Direct Offering	Warrants	Accumulated Deficit	Direct Offering	ATM offering	Total
Balance at Dec. 31, 2017			$ 1,444,056		$ 3,823	$ (926,606)			$ 521,273
Balance (in shares) at Dec. 31, 2017			337,051,000
Increase (Decrease) in Shareholders' Equity
Stock-based compensation			$ 396						396
Exercise of stock options			$ 45						$ 45
Exercise of stock options (in shares)			39,000						39,199
Shareholder distribution			$ (1,686)						$ (1,686)
Shares issued for acquisition of mineral property interests			$ 391						391
Shares issued for acquisition of mineral property interests (in shares)			178,000
Net loss						(10,591)			(10,591)
Balance at Jun. 30, 2018			$ 1,443,202		3,823	(937,197)			509,828
Balance (in shares) at Jun. 30, 2018			337,268,000
Balance at Mar. 31, 2018			$ 1,442,613		3,823	(931,817)			514,619
Balance (in shares) at Mar. 31, 2018			337,086,000
Increase (Decrease) in Shareholders' Equity
Stock-based compensation			$ 193						193
Exercise of stock options			$ 5						5
Exercise of stock options (in shares)			4,000
Shares issued for acquisition of mineral property interests			$ 391						391
Shares issued for acquisition of mineral property interests (in shares)			178,000
Net loss						(5,380)			(5,380)
Balance at Jun. 30, 2018			$ 1,443,202		3,823	(937,197)			509,828
Balance (in shares) at Jun. 30, 2018			337,268,000
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 issued during the period								$ 1,900
Balance at Mar. 31, 2019			$ 1,477,342		2,467	(981,612)			498,197
Balance (in shares) at Mar. 31, 2019			359,986,000
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			$ 197						197
Stock issued during the period	$ 20,276	$ 1,851	20,300	$ 2,634	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			$ 260						$ 260
Exercise of stock options (in shares)			258,000						257,500
Net loss						(23,150)			$ (23,150)
Balance at Jun. 30, 2019			$ 1,480,006		2,634	(994,626)			488,014
Balance (in shares) at Jun. 30, 2019			361,957,000
Balance at Mar. 31, 2019			$ 1,477,342		2,467	(981,612)			498,197
Balance (in shares) at Mar. 31, 2019			359,986,000
Increase (Decrease) in Shareholders' Equity
Stock-based compensation			$ 136						136
Stock issued during the period	$ 2,491			$ 167			$ 2,658
Stock issued during the period (in shares)	1,935,000
Exercise of stock options			$ 37						37
Exercise of stock options (in shares)			36,000
Net loss						(13,014)			(13,014)
Balance at Jun. 30, 2019			$ 1,480,006		$ 2,634	$ (994,626)			$ 488,014
Balance (in shares) at Jun. 30, 2019			361,957,000