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		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Related Party Transaction [Line Items]
Operating and maintenance expenses	$ 16.7	$ 13.4	$ 47.5	$ 36.3
General and administrative expenses	3.9	3.7	11.2	10.5
Total	$ 20.6	$ 17.1	$ 58.7	$ 46.8