Revenues from Contracts with Customers - Disaggregation of Revenue by Identified Revenue Stream (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Disaggregation of Revenue [Line Items]
Total Revenue	$ 424,035	$ 547,769	$ 1,267,629	$ 2,013,821
Natural Gas, NGLs and Oil Sales
Disaggregation of Revenue [Line Items]
Total Revenue	381,553	474,754	1,162,907	1,709,987
Natural Gas, NGLs and Oil Sales | Natural gas sales
Disaggregation of Revenue [Line Items]
Total Revenue	211,638	284,980	679,094	1,063,323
Natural Gas, NGLs and Oil Sales | NGLs sales
Disaggregation of Revenue [Line Items]
Total Revenue	149,263	143,195	416,885	508,035
Natural Gas, NGLs and Oil Sales | Oil sales
Disaggregation of Revenue [Line Items]
Total Revenue	20,652	46,579	66,928	138,629
Brokered Natural Gas, Marketing and Other
Disaggregation of Revenue [Line Items]
Total Revenue	42,482	73,015	104,722	303,834
Brokered Natural Gas, Marketing and Other | Natural gas sales
Disaggregation of Revenue [Line Items]
Total Revenue	39,180	70,404	94,364	293,209
Brokered Natural Gas, Marketing and Other | NGLs sales
Disaggregation of Revenue [Line Items]
Total Revenue	1,084	(183)	3,230	1,425
Brokered Natural Gas, Marketing and Other | Other marketing revenue
Disaggregation of Revenue [Line Items]
Total Revenue	$ 2,218	$ 2,794	$ 7,128	$ 9,200