Summary of Significant Accounting Policies (Details)				12 Months Ended
		Oct. 06, 2020 USD ($)	May 29, 2020	Dec. 31, 2020 USD ($) shares	Dec. 31, 2019 USD ($) shares	Dec. 31, 2018 shares	Dec. 31, 2016 shares	Dec. 31, 2015 shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Reverse recapitalization, conversion ratio			0.112		0.112
Net loss				$ 136,392,000	$ 98,895,000
Net cash used in operating activities				110,508,000	59,771,000
Cash				56,363,000	6,220,000
Working capital				90,300,000
Liabilities				216,009,000	573,888,000
Accumulated deficit	[1]			520,759,000	444,438,000
Proceeds from Public Offering		$ 83,100,000		83,515,000	0
Debt, amount due in next 12 months				9,100,000
Cash equivalents				0	0
Restricted cash				39,677,000	42,747,000
Impairment on equipment not in use - Note 5				5,331,000	63,000
Asset impairment charges				0
Mineral properties				$ 40,000.00	$ 0
Royalty obligation, proposed mine plan, term				34 years
Held-for-sale
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Impairment on equipment not in use - Note 5				$ 5,300,000
Non-employee director phantom stock plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares of common stock considered for cash payment of grants issued | shares				1	1	1	1	1

[1] Retroactively restated for the reverse recapitalization as described in Note 2 - Summary of Significant Accounting Policies.