New Accounting Standards - Schedule of Impact of Adoption of New Revenue Recognition Standard (Detail) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018 USD ($) $ / Mcfe	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($) $ / Mcfe	Jun. 30, 2017 USD ($)
Revenues and other income:
Natural gas, NGLs and oil sales	$ 661,390	$ 506,137	$ 1,358,019	$ 1,065,587
Natural gas, NGLs and oil sales (in dollars per share) | $ / Mcfe	3.30		3.42
Costs and expenses:
Transportation, gathering, processing and compression	$ 269,910	191,590	$ 514,538	369,238
Transportation, gathering, processing and compression (in dollars per share) | $ / Mcfe	1.35		1.29
Net (loss) income	$ (79,836)	$ 69,550	$ (30,598)	$ 239,661
Accounting Standards Update 2014-09 | Previous Revenue Recognition
Revenues and other income:
Natural gas, NGLs and oil sales	$ 619,244		$ 1,278,046
Natural gas, NGLs and oil sales (in dollars per share) | $ / Mcfe	3.09		3.22
Costs and expenses:
Transportation, gathering, processing and compression	$ 227,764		$ 434,565
Transportation, gathering, processing and compression (in dollars per share) | $ / Mcfe	1.14		1.09
Net (loss) income	$ (79,836)		$ (30,598)
Accounting Standards Update 2014-09 | Increase
Revenues and other income:
Natural gas, NGLs and oil sales	$ 42,146		$ 79,973
Natural gas, NGLs and oil sales (in dollars per share) | $ / Mcfe	0.21		0.20
Costs and expenses:
Transportation, gathering, processing and compression	$ 42,146		$ 79,973
Transportation, gathering, processing and compression (in dollars per share) | $ / Mcfe	0.21		0.20
Net (loss) income	$ 0		$ 0