Accounting Standards - Schedule of Impact of Adoption of New Revenue Recognition Standard (Detail) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2018 USD ($) $ / Mcfe	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Revenues:
Revenues									$ 3,333,836
Natural gas, NGLs and oil sales | $ / Mcfe									3.55
Costs and expenses:
Transportation, gathering, processing and compression | $ / Mcfe									1.39
Net loss	$ (1,764,422)	$ 48,539	$ (79,836)	$ 49,238	$ 221,185	$ (127,700)	$ 69,550	$ 170,111	$ (1,746,481)	$ 333,146	$ (521,388)
Accounting Standards Update 2014-09 | Previous Revenue Recognition
Revenues:
Natural gas, NGLs and oil sales | $ / Mcfe									3.33
Costs and expenses:
Transportation, gathering, processing and compression | $ / Mcfe									1.17
Net loss									$ (1,746,481)
Accounting Standards Update 2014-09 | Increase
Revenues:
Natural gas, NGLs and oil sales | $ / Mcfe									0.22
Costs and expenses:
Transportation, gathering, processing and compression | $ / Mcfe									0.22
Natural Gas, NGLs and Oil Sales
Revenues:
Revenues	756,627	736,431	661,390	696,629	603,159	507,541	506,137	559,450	$ 2,851,077	2,176,287	1,197,215
Natural Gas, NGLs and Oil Sales | Accounting Standards Update 2014-09 | Previous Revenue Recognition
Revenues:
Revenues									2,678,278
Natural Gas, NGLs and Oil Sales | Accounting Standards Update 2014-09 | Increase
Revenues:
Revenues									172,799
Transportation, Gathering, Processing and Compression
Costs and expenses:
Costs and expenses	$ 298,716	$ 304,562	$ 269,910	$ 244,628	$ 200,300	$ 191,645	$ 191,590	$ 177,648	1,117,816	$ 761,183	$ 565,209
Transportation, Gathering, Processing and Compression | Accounting Standards Update 2014-09 | Previous Revenue Recognition
Costs and expenses:
Costs and expenses									945,017
Transportation, Gathering, Processing and Compression | Accounting Standards Update 2014-09 | Increase
Costs and expenses:
Costs and expenses									$ 172,799