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Note 6 - Business Segments and Sales of Products - Sales from Continuing Operations to Significant Metals Customers As a Percentage of Total Sales (Details) - Customer Concentration Risk [Member] - Revenue from Contract with Customer Benchmark [Member]	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
CIBC [Member]
Significant metal customers	36.00%	26.00%	24.00%	34.00%
Percentage of sales	36.00%	26.00%	24.00%	34.00%
Scotia [Member]
Significant metal customers	18.00%	19.00%	26.00%	13.00%
Percentage of sales	18.00%	19.00%	26.00%	13.00%
Korea Zinc [Member]
Significant metal customers	9.00%	15.00%	16.00%	22.00%
Percentage of sales	9.00%	15.00%	16.00%	22.00%
Teck Metals Ltd [Member]
Significant metal customers	3.00%	11.00%	7.00%	11.00%
Percentage of sales	3.00%	11.00%	7.00%	11.00%
Cliveden [Member]
Significant metal customers	12.00%	0.00%	4.00%	0.00%
Percentage of sales	12.00%	0.00%	4.00%	0.00%
Trafigura [Member]
Significant metal customers	0.00%	10.00%	4.00%	3.00%
Percentage of sales	0.00%	10.00%	4.00%	3.00%

X

- Definition

For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 50
-Paragraph 18
-URI http://asc.fasb.org/extlink&oid=99393423&loc=d3e6351-108592

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 20
-URI http://asc.fasb.org/extlink&oid=118260190&loc=d3e13531-108611

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 21
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=118260190&loc=d3e13537-108611

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 50
-Paragraph 20
-URI http://asc.fasb.org/extlink&oid=99393423&loc=d3e6404-108592

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