Related Party Transactions - Summary of Classification of Charges between Operating and Maintenance Expenses and General and Administrative Expenses (Detail) - Hess - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Related Party Transaction [Line Items]
Operating and maintenance expenses	$ 15.3	$ 12.3	$ 30.8	$ 22.9
General and administrative expenses	3.5	3.2	7.3	6.8
Total	$ 18.8	$ 15.5	$ 38.1	$ 29.7