Partners' Equity (Incentive Distribution Rights) (Details) - USD ($)			12 Months Ended
	Sep. 29, 2017	Aug. 04, 2014	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Aug. 30, 2017
Class of Stock [Line Items]
Proceeds from secondary public offering, net of finance and other offering costs	$ 110,739,000		$ 110,698,000	$ 0	$ 0
Underwriting Discounts, Structuring Fees and Offering Expenses on Issuance of Equity	$ 3,111,000
Subordinated units [Member] | Westlake [Member]
Class of Stock [Line Items]
Units outstanding			0	12,686,115		12,686,115
Limited Partner [Member]
Class of Stock [Line Items]
Number of units sold in public offering	5,175,000	12,937,500
Partners' Capital Account, Units, Sold in Public Offering, Price per Unit	$ 22.00