Related Party Transactions - Summary of Revenues From Contracts With Customers on Disaggregated Basis (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Disaggregation Of Revenue [Line Items]
Total revenues from contracts with customers	$ 288.8	$ 290.6
Other income		0.2
Total revenues	288.8	290.8
Oil and Gas Gathering Services
Disaggregation Of Revenue [Line Items]
Total revenues from contracts with customers	128.7	117.4
Processing and Storage Services
Disaggregation Of Revenue [Line Items]
Total revenues from contracts with customers	103.5	96.8
Terminaling and Export Services
Disaggregation Of Revenue [Line Items]
Total revenues from contracts with customers	32.6	52.2
Water Gathering and Disposal Services
Disaggregation Of Revenue [Line Items]
Total revenues from contracts with customers	$ 24.0	$ 24.2