Partners' Capital (Details) - USD ($) $ / shares in Units, $ in Millions				1 Months Ended	3 Months Ended
	May 22, 2017	Jan. 25, 2017	Oct. 14, 2015	Apr. 30, 2017	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Dec. 31, 2015	Dec. 06, 2016
Limited Partners' Capital Account [Line Items]
Class B preferred units, outstanding					31,000,887	31,000,887
Common units, outstanding					15,171,946	14,965,134
Units, issued					15,171,946	14,965,134
Class B preferred units, issued					31,000,887	31,000,887
Class B preferred units
Limited Partners' Capital Account [Line Items]
Class B preferred units, outstanding					31,000,887
Units, issued													9,851,996
Units sold (in units)	184,697		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
Common units
Limited Partners' Capital Account [Line Items]
Common units, outstanding					15,171,946
Units, issued				84,577
Units sold (in units)						210,978	186,942	170,497	139,110	154,737	170,750
Proceeds from common units sold				$ 1.3
Common units authorized for sale, value				$ 50.0
Minimum | Class B preferred units
Limited Partners' Capital Account [Line Items]
Preferred unit conversion, amount					$ 17.5