Percentage investment held by members or limited partners of limited liability company (LLC) or limited partnership (LP).

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 272
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=6373374&loc=d3e70478-108055

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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.

+ Details

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- Definition

The number of units sold in a public offering of each class of partners' capital account. Units represent shares of ownership of the general, limited, and preferred partners.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.3-04)
-URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 5
-Subparagraph (SAB Topic 4.F)
-URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187171-122770

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- Definition

Cash outflow related to the acquisition or continued holding of limited partnership interests held for investment purposes.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
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- Definition

Limited Liability Company (LLC) or Limited Partnership (LP), Members or Limited Partners, Additional Ownership Interest

+ References

No definition available.

+ Details

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Balance Type:	na
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- Definition

Number of Production Facilities

+ References

No definition available.

+ Details

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Namespace Prefix:	wlkp_
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Balance Type:	na
Period Type:	instant

- Definition

Partners' Capital Account, Units, Sold in Public Offering, Price per Unit

+ References

No definition available.

+ Details

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Namespace Prefix:	wlkp_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	duration

- Definition

Underwriting Discounts, Structuring Fees and Offering Expenses on Issuance of Equity

+ References

No definition available.

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Description of Business and Basis of Presentation (Details) $ / shares in Units, $ in Thousands	Sep. 30, 2017	Sep. 29, 2017 USD ($) $ / shares shares	Apr. 29, 2015 USD ($)	Apr. 01, 2015	Aug. 04, 2014 shares	Jun. 30, 2018 production_facility
Limited Partners' Capital Account [Line Items]
Underwriting discounts, structuring fees and offering expenses on issuance of equity		$ 3,111
Westlake Chemical OpCo LP [Member] \| Affiliated Entity [Member]
Limited Partners' Capital Account [Line Items]
Limited partner interest	18.30%	18.30%		13.30%	10.60%
Limited partner interest, additional ownership		5.00%		2.70%
Amount paid to purchase additional limited partner interest		$ 229	$ 135,341
Westlake Chemical OpCo GP LLC [Member] \| Limited Liability Company [Member]
Limited Partners' Capital Account [Line Items]
Limited partner interest					100.00%
Westlake [Member] \| Westlake Chemical OpCo LP [Member] \| Majority-Owned Subsidiary, Unconsolidated [Member]
Limited Partners' Capital Account [Line Items]
Limited partner interest		81.70%		81.70%
Westlake Chemical OpCo LP [Member]
Limited Partners' Capital Account [Line Items]
Number of ethylene production facilities \| production_facility						3
Limited Partner [Member]
Limited Partners' Capital Account [Line Items]
Number of units sold in public offering \| shares		5,175,000			12,937,500
Units sold in secondary offering price per unit (in dollars per share) \| $ / shares		$ 22.00