Annual report pursuant to Section 13 and 15(d)

Income taxes (Schedule of Deferred Tax Assets and (Liabilities)) (Details)

v3.21.1
Income taxes (Schedule of Deferred Tax Assets and (Liabilities)) (Details) - USD ($)
$ in Thousands
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Deferred income tax assets:      
Net operating loss carryforwards $ 51,938 $ 43,436  
Research and development credit carryforwards 1,063 989  
Stock option expense 1,253 1,095  
Impairment of mining related assets and other 803 (146)  
Total deferred tax assets 55,057 45,374  
Valuation allowance (55,057) (45,374)  
Net deferred tax assets  
Deferred income tax liabilities:      
Net deferred tax liabilities     $ (143)