SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Products, Properties and Production of Minerals (Details) - home	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2018
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES
Option to sell prior to the completion of refining (as a percent)		90.00%
Number of townhomes purchased	50
Minimum
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES
Period over which concentrates are provisionally priced at the end of a period after delivery to the customer		30 days
Maximum
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES
Period over which concentrates are provisionally priced at the end of a period after delivery to the customer		90 days