Fair Value Measurements - Property Impairments (Detail) - USD ($) $ in Thousands	3 Months Ended																12 Months Ended
	Dec. 31, 2018	[1]	Sep. 30, 2018	[1]	Jun. 30, 2018	[1]	Mar. 31, 2018	[1]	Dec. 31, 2017	[1]	Sep. 30, 2017	[1]	Jun. 30, 2017		Mar. 31, 2017	[1]	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Sep. 30, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Proved property impairments																	$ 18,037	$ 82,340	$ 2,895
Unproved property impairments																	107,173	155,030	234,397
Total	$ 38,494		$ 23,770		$ 29,162		$ 33,784		$ 27,552		$ 35,130		$ 123,316	[1]	$ 51,372		$ 125,210	237,370	$ 237,292
Estimated fair value of proved properties													$ 72,000							$ 700
Arkoma Woodford [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Proved property impairments																		81,200
Non-core [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Proved property impairments																		$ 1,100

[1] Property impairments have been shown separately to illustrate the impact on quarterly results attributable to write downs of the Company’s assets. Commodity price fluctuations each quarter can result in significant changes in estimated future cash flows and resulting impairments, which affects comparability between periods.