Supplemental Oil and Gas Information (Unaudited) - Additional Information (Detail) - Bcfe	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Supplemental Oil And Gas Reserve Information [Line Items]
Percent of discount factor to proved reserves	10.00%
Reduction in reserves	351.0	415.4
Downward price revisions in proved reserve	148.3	413
Downward revisions due to updated well performance data	87.9	13
Divestiture of oil and gas properties	35.3
Multiple acquisitions		97.1	561.7
2015 Beta Acquisition [Member]
Supplemental Oil And Gas Reserve Information [Line Items]
Multiple acquisitions, Largest acquisition		58.5
Wyoming Acquisition [Member]
Supplemental Oil And Gas Reserve Information [Line Items]
Multiple acquisitions, Largest acquisition			497.2
Eagle Ford Acquisition [Member]
Supplemental Oil And Gas Reserve Information [Line Items]
Multiple acquisitions			45.0