Investments - Summary of Investments (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Schedule of Equity Method Investments [Line Items]
Investments	$ 871,030	$ 660,778
White Cliffs
Schedule of Equity Method Investments [Line Items]
Investments	10,115	10,268
Advantage Joint Venture
Schedule of Equity Method Investments [Line Items]
Investments	75,139	76,834
Delaware Crossing Joint Venture
Schedule of Equity Method Investments [Line Items]
Investments	85,423	68,707
Saddlehorn
Schedule of Equity Method Investments [Line Items]
Investments	159,744	0
EPIC Propane
Schedule of Equity Method Investments [Line Items]
Investments	4,503	3,003
EPIC Y-Grade
Schedule of Equity Method Investments [Line Items]
Investments	171,221	162,850
EPIC Crude
Schedule of Equity Method Investments [Line Items]
Investments	$ 364,885	$ 339,116