Acquisitions - Additional Information (Detail) $ / shares in Units, $ in Thousands			3 Months Ended	12 Months Ended
	Feb. 28, 2019 USD ($) $ / shares shares	Jan. 18, 2018 USD ($) a Well shares	Mar. 31, 2019 $ / shares	Dec. 31, 2018 $ / shares	Mar. 31, 2018 $ / shares	Dec. 31, 2017 $ / shares
Business Acquisition [Line Items]
Common stock, par value | $ / shares			$ 0.01	$ 0.01	$ 0.01	$ 0.01
Reverse stock split			0.067
Flat Castle Acquisition [Member]
Business Acquisition [Line Items]
Area of land purchased | a		44,500
Purchase price		$ 90,000
Purchase price paid through shares of common stock | shares		2,500,000
Transaction costs capitalized related to acquisition		$ 1,000
Flat Castle Acquisition [Member] | Proved Oil And Gas Properties [Member]
Business Acquisition [Line Items]
Number of producing wells acquired | Well		1
Purchase price		$ 4,000
Flat Castle Acquisition [Member] | Unproved Oil and Natural Gas Properties [Member]
Business Acquisition [Line Items]
Purchase price		$ 86,000
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]
Business Acquisition [Line Items]
Purchase price	$ 275,759
Common stock, par value | $ / shares	$ 0.01
BRMR and Everest Merger Sub Inc. [Member] | Common Stock [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	0.067