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Note 10 - Debt, Credit Facility and Capital Leases (Details Textual) $ in Millions |  |  | 9 Months Ended | 12 Months Ended |  |  |  |  |
--- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Jul. 31, 2018 USD ($) | Apr. 12, 2013 USD ($) | Sep. 30, 2018 USD ($) | Sep. 30, 2017 USD ($) | Dec. 31, 2014 USD ($) | Jan. 01, 2020 | Jul. 20, 2018 USD ($) | Mar. 05, 2018 USD ($) | Mar. 05, 2018 CAD ($) | Dec. 31, 2017 USD ($) | May 31, 2016 USD ($)
Letters of Credit Outstanding, Amount |  |  |  | $ 3,000,000 |  |  |  |  |  |  |  |
Capital Lease Obligations, Total |  |  |  | 14,656,000 |  |  |  |  |  |  | $ 11,800,000 |
Capital Lease Obligations, Current |  |  |  | 6,069,000 |  |  |  |  |  |  | 5,608,000 |
Capital Lease Obligations, Noncurrent |  |  |  | 8,638,000 |  |  |  |  |  |  | $ 6,193,000 |
Capital Leases, Future Minimum Payments Due, Total |  |  |  | 15,675,000 |  |  |  |  |  |  |  |
Capital Leases, Future Minimum Payments, Interest Included in Payments |  |  |  | $ 1,019,000 |  |  |  |  |  |  |  |
Klondex Mines Ltd [Member] |  |  |  |  |  |  |  |  |  |  |  |
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities, Long-term Debt |  |  |  |  |  |  |  | $ 35,086,000 |  |  |  |
Maximum [Member] |  |  |  |  |  |  |  |  |  |  |  |
Leverage Ratio | [1] |  |  | 4.5 |  |  |  |  |  |  |  |
Revolving Credit Facility [Member] |  |  |  |  |  |  |  |  |  |  |  |
Line of Credit Facility, Current Borrowing Capacity |  | $ 200,000,000 |  |  |  |  |  |  |  |  |  |
Line of Credit Facility, Maximum Borrowing Capacity |  | 250,000,000 |  |  |  |  |  |  |  |  |  | $ 100,000,000
Long-term Line of Credit, Total |  | 47,000,000 |  | $ 0 |  |  |  |  |  |  |  |
Revolving Credit Facility [Member] | Klondex Mines Ltd [Member] |  |  |  |  |  |  |  |  |  |  |  |
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities, Long-term Debt |  |  |  |  |  |  |  | $ 35,000,000 |  |  |  |
Repayments of Lines of Credit |  | $ 35,000,000 |  |  |  |  |  |  |  |  |  |
Revolving Credit Facility [Member] | Scenario, Forecast [Member] |  |  |  |  |  |  |  |  |  |  |  |
Leverage Ratio |  |  |  |  |  |  | 4 |  |  |  |  |
Letter of Credit [Member] |  |  |  |  |  |  |  |  |  |  |  |
Letter of Credit Outstanding, Fronting Fee |  | 0.20% |  |  |  |  |  |  |  |  |  |
Letter of Credit [Member] | Minimum [Member] |  |  |  |  |  |  |  |  |  |  |  |
Letter of Credit, Participation Fee, Percent |  | 2.25% |  |  |  |  |  |  |  |  |  |
Letter of Credit [Member] | Maximum [Member] |  |  |  |  |  |  |  |  |  |  |  |
Letter of Credit, Participation Fee, Percent |  | 3.25% |  |  |  |  |  |  |  |  |  |
Senior Notes [Member] |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument, Face Amount |  |  | $ 500,000,000 |  |  |  |  |  |  |  |  |
Payment for Pension Benefits |  |  |  |  |  | $ 6,500,000 |  |  |  |  |  |
Proceeds from Issuance of Senior Long-term Debt |  |  | $ 490,000,000 |  |  |  |  |  |  |  |  |
Underwriting Discount on Senior Notes |  |  | 2.00% |  |  |  |  |  |  |  |  |
Debt Instrument, Unamortized Discount, Total |  |  | $ 10,000,000 | 3,300,000 |  |  |  |  |  |  |  |
Debt Instrument, Interest Rate, Stated Percentage |  |  | 6.875% |  |  |  |  |  |  |  |  |
Interest Expense, Debt, Total |  |  |  | $ 27,200,000 | $ 26,300,000 |  |  |  |  |  |  |
Interest Costs Capitalized |  |  |  |  | 900,000 |  |  |  |  |  |  |
Debt Instrument, Redemption Price, Percentage |  |  |  | 101.00% |  |  |  |  |  |  |  |
Senior Notes [Member] | Costs Related to Private Offering and Tender Offer [Member] |  |  |  |  |  |  |  |  |  |  |  |
Interest Expense, Debt, Total |  |  |  |  | $ 1,100,000 |  |  |  |  |  |  |
Series 2018-A Senior Notes [Member] |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument, Face Amount |  |  |  |  |  |  |  |  | $ 30,800,000 | $ 40.0 |  |
Debt Instrument, Unamortized Discount, Total |  |  |  |  |  |  |  |  |  | $ 0.2 |  |
Debt Instrument, Interest Rate, Stated Percentage |  |  |  |  |  |  |  |  | 4.68% | 4.68% |  |
Interest Expense, Debt, Total |  |  |  | $ 1,100,000 |  |  |  |  |  |  |  |
Debt Instrument, Issuance, Discount Rate |  |  |  |  |  |  |  |  | 0.58% | 0.58% |  |
[1] | The leverage ratio will change to 4.00:1 effective January 1, 2020.

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- Definition Amount equal to the present value (the principal) at the beginning of the lease term of minimum lease payments during the lease term (excluding that portion of the payments representing executory costs such as insurance, maintenance, and taxes to be paid by the lessor, together with any profit thereon) net of payments or other amounts applied to the principal through the balance sheet date. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(22)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 840 -SubTopic 30 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=84164817&loc=d3e45280-112737 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03(a)(16)) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 + Details
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