Fair Value Measurements - Property Impairments (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Proved property impairments	$ 0	$ 0	$ 0	$ 82,340
Unproved property impairments	23,770	35,130	86,715	127,479
Oil and gas property fair value after impairment		72,000		72,000
Property impairments	$ 23,770	$ 35,130	$ 86,715	209,819
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