Revenues from Contracts with Customers - Disaggregation of Revenue by Identified Revenue Stream (Parenthetical) (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($)
Disaggregation of Revenue [Line Items]
Revenues	$ 3,333,836
Natural gas sales
Disaggregation of Revenue [Line Items]
Revenues	2,137,573	[1]
NGLs sales
Disaggregation of Revenue [Line Items]
Revenues	940,378	[2]
Brokered | Natural gas sales
Disaggregation of Revenue [Line Items]
Revenues	460,300
Brokered | NGLs sales
Disaggregation of Revenue [Line Items]
Revenues	9,000
Marketing | Natural gas sales
Disaggregation of Revenue [Line Items]
Revenues	$ 13,400

[1] Natural gas sales revenue reported above includes $460.3 million of brokered revenues and $13.4 million of marketing revenue.

[2] NGLs sales revenue reported above includes $9.0 million of brokered revenues.