CONSOLIDATED STATEMENTS OF CHANGES IN SHAREHOLDERS' EQUITY - USD ($) $ in Thousands	Common Stock and Additional Paid-in Capital	Accumulated Deficit	Total
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	$ 61		61
Exercise of stock options	$ 223		$ 223
Exercise of stock options (in shares)	222,000		221,500
Units Issued for cash, net of share issue cost	$ 20,252		$ 20,252
Units Issued for cash, net of share issue cost (in shares)	14,194,000
Shares issued for acquisition of mineral property interests	$ 1,851		1,851
Shares issued for acquisition of mineral property interests (in shares)	1,010,000
Net loss		(10,136)	(10,136)
Balance at Mar. 31, 2019	$ 1,479,809	(981,612)	498,197
Balance (in shares) at Mar. 31, 2019	359,986,000
Balance at Dec. 31, 2019	$ 1,530,702	(1,031,223)	499,479
Balance (in shares) at Dec. 31, 2019	400,339,000
Increase (Decrease) in Shareholders' Equity
Stock-based compensation	$ 88		88
Exercise of stock options	$ 62		$ 62
Exercise of stock options (in shares)	60,000		60,000
Net loss		(99,191)	$ (99,191)
Balance at Mar. 31, 2020	$ 1,530,852	$ (1,130,414)	$ 400,438
Balance (in shares) at Mar. 31, 2020	400,399,000