Distributions and Net Income Per Limited Partner Unit (Tables)

12 Months Ended

Dec. 31, 2017

Earnings Per Share [Abstract]

Schedule of Incentive Distributions Made to Managing Members or General Partners by Distribution

If cash distributions to the Partnership's unitholders exceed $0.3163 per unit in any quarter, the Partnership's unitholders and Westlake, as the holder of the Partnership's incentive distribution rights, will receive distributions according to the following percentage allocations:

	Marginal Percentage Interest in Distributions
Total Quarterly Distribution Per Unit	Unitholders		IDR Holders
Above $0.3163 up to $0.3438	85.0	%	15.0	%
Above $0.3438 up to $0.4125	75.0	%	25.0	%
Above $0.4125	50.0	%	50.0	%

Schedule of Earnings Per Share, Basic and Diluted

	Year Ended December 31
	2017		2016		2015
Net income attributable to the Partnership	$	48,670	$	40,940	$	39,831
Less:
Limited partners' distribution declared on common units	34,909		19,016		16,980
Limited partners' distribution declared on subordinated units	9,133		16,784		14,986
Distributions declared with respect to the incentive distribution rights	1,666		281		—
Net income in excess of distribution	$	2,962	$	4,859	$	7,865

Net income per unit applicable to common limited partner units and to subordinated limited partner units is computed by dividing the respective limited partners' interest in net income by the weighted-average number of common units and subordinated units outstanding for the period. Because the Partnership has more than one class of participating securities, it uses the two-class method when calculating the net income per unit applicable to limited partners. The classes of participating securities include common units, subordinated units and incentive distribution rights. Net income attributable to the Partnership is allocated to the unitholders in accordance with their respective ownership percentages in preparation of the consolidated statements of changes in equity. However, when distributions related to the incentive distribution rights are made, net income equal to the amount of those distributions is first allocated to the general partner before the remaining net income is allocated to the unitholders based on their respective ownership percentages. Basic and diluted net income per unit is the same because the Partnership does not have any potentially dilutive units outstanding for the periods presented.

As discussed further in Note 9, the 12,686,115 subordinated units, all of which were owned by Westlake, were converted into common units effective August 30, 2017. For purposes of calculating net income per unit, the subordinated units were treated as if they had been converted to common units on July 1, 2017. Therefore, the subordinated units did not share in the distribution of cash generated from July 1, 2017 to December 31, 2017, and the Partnership did not allocate any earnings to the subordinated unitholders from July 1, 2017 to December 31, 2017 for the determination of net income per unit.

	December 31, 2017
	Limited Partners' Common Units		Limited Partners' Subordinated Units			Incentive Distribution Rights		Total
Net income attributable to the Partnership:
Distribution	$	34,909	$	9,133		$	1,666	$	45,708
Net income in excess of distribution (distribution in    excess of net income)	3,101		(139		)	—		2,962
Net income	$	38,010	$	8,994		$	1,666	$	48,670
Weighted average units outstanding:
Basic and diluted	22,101,547		6,290,923					28,392,470
Net income per limited partner unit:
Basic and diluted	$	1.72	$	1.43

	December 31, 2016
	Limited Partners' Common Units		Limited Partners' Subordinated Units		Incentive Distribution Rights		Total
Net income attributable to the Partnership:
Distribution	$	19,016	$	16,784	$	281	$	36,081
Net income in excess of distribution	2,581		2,278		—		4,859
Net income	$	21,597	$	19,062	$	281	$	40,940
Weighted average units outstanding:
Basic and diluted	14,373,615		12,686,115				27,059,730
Net income per limited partner unit:
Basic and diluted	$	1.50	$	1.50

	December 31, 2015
	Limited Partners' Common Units		Limited Partners' Subordinated Units		Incentive Distribution Rights		Total
Net income attributable to the Partnership:
Distribution	$	16,980	$	14,986	$	—	$	31,966
Net income in excess of distribution	4,178		3,687		—		7,865
Net income	$	21,158	$	18,673	$	—	$	39,831
Weighted average units outstanding:
Basic and diluted	14,373,615		12,686,115				27,059,730
Net income per limited partner unit:
Basic and diluted	$	1.47	$	1.47