Income taxes - Components of Deferred Tax Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2025	Dec. 31, 2024
Income Tax Disclosure [Abstract]
Net operating loss	$ 80,863	$ 74,056
Mineral properties	56,198	52,303
Plant, equipment, and mine development	1,687	1,415
Intangible assets	14,181	15,687
Deferred gain on sale of royalty	6,266	6,266
Asset retirement obligation	2,472	2,762
Interest expense carryforward	8,799	9,156
Accrued compensation	663	629
Stock-based compensation	1,927	1,998
Inventories	943	947
Assets held-for-sale	(39)	476
Other	895	990
Valuation allowance	(174,855)	(166,685)
Total	$ 0	$ 0

Deferred Tax Assets, Mineral Properties

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- Definition

Deferred Tax Assets, Royalty

+ References

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- Definition

Deferred Tax Liabilities, Available For Sale Assets

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- Definition

Amount, before allocation of valuation allowance, of deferred tax asset attributable to deductible interest carryforward.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482685/740-10-50-6

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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from intangible assets including goodwill.

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- Definition

Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from inventory.

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- Definition

Amount, after allocation of valuation allowances and deferred tax liability, of deferred tax asset attributable to deductible differences and carryforwards, without jurisdictional netting.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482685/740-10-50-2

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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible operating loss carryforwards.

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Amount, before allocation of valuation allowance, of deferred tax asset attributable to deductible temporary differences, classified as other.

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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from property, plant, and equipment.

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Amount, before allocation of valuation allowance, of deferred tax asset attributable to deductible temporary differences from compensation and benefits, classified as other.

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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from share-based compensation.

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- Definition

Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from asset retirement obligations. An asset retirement obligation is a legal obligation associated with the disposal or retirement from service of a tangible long-lived asset.

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- Definition

Amount of deferred tax assets for which it is more likely than not that a tax benefit will not be realized.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482685/740-10-50-2

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