Long-Term Reclamation Liability - Reconciliation of Aggregate Retirement Liability (Details) - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Mine Reclamation and Closing Liability [Roll Forward]
Long-term reclamation liability — beginning of period	$ 7,441,091	$ 7,417,680
Additional obligations incurred	0	0
Accretion of reclamation liability	5,710	23,411
Long-term reclamation liability — end of period	$ 7,446,801	$ 7,441,091