Revenues from Contracts with Customers - Disaggregation of Revenue by Identified Revenue Stream (Parenthetical) (Detail) - USD ($) $ in Thousands		3 Months Ended	9 Months Ended
		Sep. 30, 2018	Sep. 30, 2018
Disaggregation of Revenue [Line Items]
Revenues		$ 845,816	$ 2,361,898
Natural gas sales
Disaggregation of Revenue [Line Items]
Revenues	[1]	500,194	1,449,148
NGLs sales
Disaggregation of Revenue [Line Items]
Revenues	[2]	278,410	706,673
Brokered | Natural gas sales
Disaggregation of Revenue [Line Items]
Revenues		105,800	255,100
Brokered | NGLs sales
Disaggregation of Revenue [Line Items]
Revenues		(153,000)	880,000
Marketing | Natural gas sales
Disaggregation of Revenue [Line Items]
Revenues		$ 3,700	$ 11,400

[1] Natural gas sales revenue reported above for the third quarter includes $105.8 million of brokered revenues and $3.7 million of marketing revenue. The nine months includes $255.1 million of brokered revenues and $11.4 million of marketing revenue.

[2] NGLs sales revenue reported above for the third quarter includes ($153,000) of brokered revenues and for nine months includes $880,000 of brokered revenues.