Commitments and Contingencies - Additional Information (Detail) - USD ($)	6 Months Ended
Jun. 30, 2019	Dec. 31, 2018
Commitments and Contingencies [Line Items]
Guarantee of affiliate's obligations	$ 15,500,000
Due from affiliate	12,700,000
Outstanding letters of credit	$ 35,300,000
Woodville
Commitments and Contingencies [Line Items]
Collective bargaining agreement expiration month year	2022-06
Magnesia Specialties
Commitments and Contingencies [Line Items]
Percentage of employees represented in labor union	100.00%
Collective bargaining agreement expiration month year	2019-08
Revolving Facility
Commitments and Contingencies [Line Items]
Maturity date	Dec. 05, 2023
Outstanding letters of credit	$ 2,300,000	$ 2,300,000
Interest-only loan
Commitments and Contingencies [Line Items]
Due from affiliate	$ 6,000,000.0	$ 6,000,000.0
Maturity date	Dec. 31, 2022
Interest-only loan \| London Interbank Offered Rate(LIBOR)
Commitments and Contingencies [Line Items]
Basis spread on variable rate	1.75%
Revolving Line Of Credit Expires In August 2015
Commitments and Contingencies [Line Items]
Line of credit maturity period	2020-03

Affiliate line of credit facility maturity period.

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- Definition

Collective bargaining agreement expiration month year.

+ References

No definition available.

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- Definition

Commitments and contingencies.

+ References

No definition available.

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- Definition

Guarantee obligations outstanding.

+ References

No definition available.

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- Definition

Percentage of employees represented in labor union.

+ References

No definition available.

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- 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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- Definition

Date when the debt instrument is scheduled to be fully repaid, in CCYY-MM-DD format.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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- Definition

For an unclassified balance sheet, amount of receivables due from an entity that is affiliated with the reporting entity by means of direct or indirect ownership.

+ References

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- Definition

Maximum potential amount of future payments (undiscounted) the guarantor could be required to make under the guarantee or each group of similar guarantees before reduction for potential recoveries under recourse or collateralization provisions.

+ References

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- Definition

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

+ References

No definition available.

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