Acquisition - Additional Information (Detail) $ / shares in Units, $ in Millions			12 Months Ended
	Feb. 28, 2019 $ / shares shares	Jan. 18, 2018 USD ($) a Well shares	Dec. 31, 2018 $ / shares	Dec. 31, 2017 $ / shares	Dec. 31, 2016 $ / shares
Business Acquisition [Line Items]
Common stock, par value | $ / shares			$ 0.01	$ 0.01	$ 0.01
Flat Castle Acquisition [Member]
Business Acquisition [Line Items]
Area of land purchased | a		44,500
Purchase price		$ 90
Purchase price paid through shares of common stock | shares		2,500,000
Transaction costs capitalized related to acquisition		$ 1
Flat Castle Acquisition [Member] | Proved Oil And Gas Properties [Member]
Business Acquisition [Line Items]
Number of producing wells acquired | Well		1
Purchase price		$ 4
Flat Castle Acquisition [Member] | Unproved Oil and Natural Gas Properties [Member]
Business Acquisition [Line Items]
Purchase price		$ 86
Cardinal Midstream II, LLC [Member]
Business Acquisition [Line Items]
Third party options exercised month and year			2018-07
BRMR and Everest Merger Sub Inc. [Member] | Subsequent Event [Member]
Business Acquisition [Line Items]
Common stock, par value | $ / shares	$ 0.01
BRMR and Everest Merger Sub Inc. [Member] | Common Stock [Member] | Subsequent Event [Member]
Business Acquisition [Line Items]
Purchase price paid through shares of common stock | shares	0.29506
Reverse stock split, description	15-to-1
Reverse stock split	0.066