Revenues from Contracts with Customers - Disaggregation of Revenue by Identified Revenue Stream (Parenthetical) (Detail) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2019	Mar. 31, 2018
Disaggregation of Revenue [Line Items]
Revenues		$ 809,868	$ 756,608
Natural gas sales
Disaggregation of Revenue [Line Items]
Revenues	[1]	572,510	491,248
NGLs sales
Disaggregation of Revenue [Line Items]
Revenues	[2]	198,237	202,831
Brokered | Natural gas sales
Disaggregation of Revenue [Line Items]
Revenues		134,800	55,900
Brokered | NGLs sales
Disaggregation of Revenue [Line Items]
Revenues		424,000	304,000
Marketing | Natural gas sales
Disaggregation of Revenue [Line Items]
Revenues		$ 3,000	$ 3,800

[1] Natural gas sales revenue reported above for first quarter 2019 includes $134.8 million of brokered revenues and $3.0 million of marketing revenue. First quarter 2018 includes $55.9 million of brokered revenues and $3.8 million of marketing revenue.

[2] NGLs sales revenue reported above for the first quarter 2019 includes $424,000 of brokered revenues and first quarter 2018 includes $304,000 of brokered revenues.