Fair Value Measurements - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Jun. 30, 2017
Fair Value Measurements [Line Items]
Operating cost escalation assumption used in impairment assessment	3.00%
Discount factor utilized as standardized measure for future net cash flows	10.00%
Impairments of proved properties	$ 82,340	$ 2,895	$ 138,878
Estimated fair value of proved properties				$ 72,000
Minimum [Member]
Fair Value Measurements [Line Items]
Productive life of field (in years)	1 year
Maximum [Member]
Fair Value Measurements [Line Items]
Productive life of field (in years)	38 years
Forward Commodity Prices [Member]
Fair Value Measurements [Line Items]
Forward commodity price escalation assumption used in impairment assessment	3.00%