New Accounting Standards - Schedule of Impact of Adoption of New Revenue Recognition Standard (Detail) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018 USD ($) $ / Mcfe	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($) $ / Mcfe	Sep. 30, 2017 USD ($)
Revenues:
Revenues	$ 845,816		$ 2,361,898
Natural gas, NGLs and oil sales | $ / Mcfe	3.53		3.45
Costs and expenses:
Transportation, gathering, processing and compression | $ / Mcfe	1.46		1.35
Net income	$ 48,539	$ (127,700)	$ 17,941	$ 111,961
Natural Gas, NGLs and Oil Sales
Revenues:
Revenues	736,431	507,541	2,094,450	1,573,128
Transportation, Gathering, Processing and Compression
Costs and expenses:
Costs and expenses	$ 304,562	$ 191,645	$ 819,100	$ 560,883
Accounting Standards Update 2014-09 | Previous Revenue Recognition
Revenues:
Natural gas, NGLs and oil sales | $ / Mcfe	3.30		3.24
Costs and expenses:
Transportation, gathering, processing and compression | $ / Mcfe	1.23		1.14
Net income	$ 48,539		$ 17,941
Accounting Standards Update 2014-09 | Increase
Revenues:
Natural gas, NGLs and oil sales | $ / Mcfe	0.23		0.21
Costs and expenses:
Transportation, gathering, processing and compression | $ / Mcfe	0.23		0.21
Net income	$ 0		$ 0
Accounting Standards Update 2014-09 | Natural Gas, NGLs and Oil Sales | Previous Revenue Recognition
Revenues:
Revenues	688,684		1,966,731
Accounting Standards Update 2014-09 | Natural Gas, NGLs and Oil Sales | Increase
Revenues:
Revenues	47,747		127,719
Accounting Standards Update 2014-09 | Transportation, Gathering, Processing and Compression | Previous Revenue Recognition
Costs and expenses:
Costs and expenses	256,815		691,381
Accounting Standards Update 2014-09 | Transportation, Gathering, Processing and Compression | Increase
Costs and expenses:
Costs and expenses	$ 47,747		$ 127,719