Long-Term Debt - Other Secured Obligations (Details) $ in Thousands	12 Months Ended
Dec. 31, 2021 USD ($) subsidiary	Dec. 31, 2020 USD ($)
Long Term Debt
Outstanding principal balance	$ 3,155,422	$ 3,158,658
Maximum borrowing capacity of credit facility	25,000
Senior secured revolving credit facility
Long Term Debt
Unused stand-by letter of credit	1,200,000
Maximum borrowing capacity of credit facility	1,200,000
Borrowings outstanding	$ 0
Two Subsidiaries [Member] \| Secured Debt [Member]
Long Term Debt
Number of subsidiaries \| subsidiary	2
Long-term Debt, Weighted Average Interest Rate, at Point in Time	4.70%
Outstanding principal balance	$ 10,400	9,600
Subsidiary One [Member] \| Revolving Credit Facility
Long Term Debt
Number of subsidiaries \| subsidiary	1
Secured letter of credit	$ 30,000
Maximum borrowing capacity of credit facility	$ 100,000
Line of Credit Facility, Interest Rate at Period End	1.60%
Borrowings outstanding	$ 94,400	82,300
Subsidiary Two [Member] \| Revolving Credit Facility
Long Term Debt
Line of Credit Facility, Interest Rate at Period End	3.00%
Borrowings outstanding	$ 0
Mesabi Nugget \| Secured Debt [Member]
Long Term Debt
Outstanding principal balance	$ 0	$ 15,200

Number Of Subsidiaries

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- Definition

Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (b)(1)
-URI http://asc.fasb.org/extlink&oid=123466204&loc=SL6031897-161870

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
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-URI http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910

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-Name Accounting Standards Codification
-Topic 210
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-Section S99
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-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
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-Subparagraph (SX 210.9-03(16))
-URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878

+ Details

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Balance Type:	credit
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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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- Definition

The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

+ 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
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-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

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+ Details

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- Definition

The effective interest rate at the end of the reporting period.

+ References

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- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

+ Details

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Balance Type:	credit
Period Type:	instant

- Definition

Amount of borrowing capacity currently available under the credit facility (current borrowing capacity less the amount of borrowings outstanding).

+ References

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- Definition

Weighted average interest rate of long-term debt outstanding calculated at point in time.

+ References

No definition available.

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- Definition

Fair value of the securities pledged as collateral against securities loaned.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 12
-URI http://asc.fasb.org/extlink&oid=99393222&loc=SL20226013-175313

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