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Fair Value Measurements - Summary of Level 3 Financial Assets and Liabilities (Details) - Silvertip Mine
$ in Thousands
3 Months Ended
Mar. 31, 2020
USD ($)
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]  
Balance at the start of the period $ 25,000
Revaluation 0
Settlements (25,000)
Accretion 0
Balance at the end of the period $ 0