Debt Instrument, Payment Terms, Number of Monthly Payments

No definition available.

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- Definition

The amount of additional borrowings provided in credit facility under a letter of credit sub-facility.

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Line of Credit Facility, Remaining Borrowing Capacity, Net of Letters of Credit

+ References

No definition available.

+ Details

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Balance Type:	credit
Period Type:	instant

- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

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Balance Type:	na
Period Type:	duration

- Definition

Face (par) amount of debt instrument at time of issuance.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
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Balance Type:	credit
Period Type:	instant

- Definition

Fair value portion of debt instrument payable, including, but not limited to, notes payable and loans payable.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=109250915&loc=d3e13433-108611

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

+ Details

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Balance Type:	na
Period Type:	instant

- Definition

Portion of the carrying amount as of the balance sheet date of obligations due all related parties that is payable after one year or beyond the normal operating cycle if longer.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
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+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

+ References

No definition available.

+ Details

Name:	us-gaap_LettersOfCreditOutstandingAmount
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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- 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

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+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of current borrowing capacity under the credit facility considering any current restrictions on the amount that could be borrowed (for example, borrowings may be limited by the amount of current assets), but without considering any amounts currently outstanding under the facility.

+ References

+ Details

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Balance Type:	credit
Period Type:	instant

- 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.

+ Details

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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

+ Details

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Balance Type:	credit
Period Type:	instant

- Definition

Carrying value as of the balance sheet date of the portion of long-term, collateralized debt obligations due within one year or the operating cycle, if longer. Such obligations include mortgage loans, chattel loans, and any other borrowings secured by assets of the borrower.

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+ Details

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Period Type:	instant

- Details

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- Details

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- Details

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Debt - Credit Facility (Details)	Apr. 29, 2019 USD ($) payment	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Jun. 04, 2013 USD ($)
Line of Credit Facility [Line Items]
Fair value of debt instrument		$ 251,300,000	$ 247,900,000
U.S. revolving credit facility [Member]
Line of Credit Facility [Line Items]
Credit facility maximum amount		175,000,000
Borrowing availability		175,000,000
Borrowing availability, net of outstanding letters of credit and borrowings		37,700,000
U.S. revolving credit facility [Member] \| Long-term Debt [Member]
Line of Credit Facility [Line Items]
Credit facility face amount		175,000,000
U.S. letter of credit [Member]
Line of Credit Facility [Line Items]
Letter of credit sub-facility amount		102,000,000
U.S. letter of credit [Member] \| Long-term Debt [Member]
Line of Credit Facility [Line Items]
Letter of credit sub-facility amount		110,000,000
U.S. revolving credit facility, accordion [Member] \| Long-term Debt [Member]
Line of Credit Facility [Line Items]
Credit facility face amount		50,000,000.0
Iceland revolving line of credit [Member] \| Long-term Debt [Member]
Line of Credit Facility [Line Items]
Credit facility maximum amount		50,000,000
Borrowing availability		50,000,000
Borrowing availability, net of outstanding letters of credit and borrowings		0
Borrowing availability, net of borrowings		$ 50,000,000
Senior secured notes due June 01, 2021 [Member] \| Long-term Debt [Member]
Line of Credit Facility [Line Items]
Face amount				$ 250,000,000
Stated interest rate, percentage		7.50%		7.50%
Short-term Debt [Member] \| U.S. letter of credit [Member]
Line of Credit Facility [Line Items]
Outstanding borrowings		$ 35,300,000
Short-term Debt [Member] \| Iceland revolving line of credit [Member]
Line of Credit Facility [Line Items]
Outstanding borrowings		0
Short-term Debt [Member] \| U.S. revolving credit facility borrowings [Member]
Line of Credit Facility [Line Items]
U.S revolving credit facility		$ 35,300,000	$ 23,300,000
Subsequent Event [Member] \| Glencore [Member]
Line of Credit Facility [Line Items]
Due to related parties, noncurrent	$ 40,000,000
Debt instrument, payment terms, number of monthly payments \| payment	24
Subsequent Event [Member] \| London Interbank Offered Rate (LIBOR) [Member] \| Glencore [Member]
Line of Credit Facility [Line Items]
Debt instrument, basis spread on variable rate	5.375%