Fair Value Measurements - Property Impairments (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Proved property impairments	$ 0	$ 81,469	$ 0	$ 82,340
Unproved property impairments	29,162	41,847	62,946	92,349
Oil and gas property fair value after impairment		72,000		72,000
Property impairments	$ 29,162	123,316	$ 62,946	174,689
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		$ 300		$ 1,100