Consolidated Balance Sheets (Parenthetical) - shares	Dec. 31, 2017	Dec. 31, 2016
Common units [Member] | Westlake [Member]
Units outstanding	14,122,230	1,436,115
Common units [Member] | Public [Member]
Units outstanding	18,112,500	12,937,500
Subordinated units [Member] | Westlake [Member]
Units outstanding	0	12,686,115