Partners' Capital (Details) - USD ($) $ / shares in Units, $ in Millions			3 Months Ended								12 Months Ended
	Jan. 25, 2017	Oct. 14, 2015	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Dec. 31, 2015	Dec. 31, 2019	Aug. 31, 2018	Dec. 06, 2016
Limited Partners' Capital Account [Line Items]
Class B preferred units, outstanding					31,310,896						0
Common units, outstanding					16,486,239						20,087,462
Units, issued					16,486,239						20,087,462
Class B preferred units, issued					31,310,896						0
Class B preferred units
Limited Partners' Capital Account [Line Items]
Units, issued												310,009	9,851,996
Units sold (in units)		19,444,445
Price per unit sold		$ 18.00
Proceeds from preferred units sold		$ 350.0
Percent of consideration paid		2.25%
Paid in full in cash, per annum										10.00%
Paid in part cash, per annum										12.00%
Dividend per annum										8.00%
Paid-in kind units per annum										4.00%
Class B preferred units | Settlement Agreement with Stonepeak Catarina Holdings LLC
Limited Partners' Capital Account [Line Items]
Class B preferred units, issued	1,704,446
Class B preferred units, unit price	$ 11.29
Class C preferred units
Limited Partners' Capital Account [Line Items]
Class B preferred units, outstanding											33,258,043
Common units
Limited Partners' Capital Account [Line Items]
Common units, outstanding											20,087,462
Units sold (in units)			901,741	887,269	787,750	334,010	224,342	220,214	210,978
Unvested restricted common units | LTIP
Limited Partners' Capital Account [Line Items]
Common units, outstanding											1,155,467
Minimum | Class B preferred units
Limited Partners' Capital Account [Line Items]
Preferred unit conversion, amount											$ 17.5