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Note 3 - Investments - Current Investments (Details) - USD ($) $ in Thousands | Sep. 30, 2018 | Dec. 31, 2017
--- | --- | ---
Fair market value | $ 0 | $ 33,758
Corporate Bond Securities [Member] |  |
Amortized cost |  | 33,778
Unrealized loss |  | (20)
Fair market value |  | $ 33,758

X
- Definition Amount before tax of current unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt securities classified as available-for-sale. + References No definition available. + Details
Name: | hl_DebtSecuritiesAvailableForSaleAccumulatedGrossUnrealizedLossBeforeTaxCurrent
Namespace Prefix: | hl_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition This item represents the current cost of debt securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any. + References No definition available. + Details
Name: | hl_DebtSecuritiesAvailableForSaleAmortizedCostBasisCurrent
Namespace Prefix: | hl_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), classified as current. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=109979856&loc=d3e26626-111562 + Details
Name: | us-gaap_AvailableForSaleSecuritiesDebtSecuritiesCurrent
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Details
Name: | us-gaap_InvestmentTypeAxis=us-gaap_CorporateBondSecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |