Quarterly report pursuant to Section 13 or 15(d)

Restricted Cash (Details)

v3.19.1
Restricted Cash (Details) - USD ($)
$ in Thousands
Mar. 31, 2019
Dec. 31, 2018
Mar. 31, 2018
Restricted Cash      
Restricted cash $ 7,460 $ 7,458 $ 7,458
Surety Bond [Member]      
Restricted Cash      
Reclamation bonding requirement 29,900    
Money Market Funds [Member] | Surety Bond [Member]      
Restricted Cash      
Restricted cash pledged as collateral $ 7,400