Discontinued Operations (Significant Operating and Investing Activities of Discontinued Operations) (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Operating activities:
Asset impairments			$ 37,900	$ 57,065
Accounts payable and other accrued liabilities			(9,235)	(13,556)
Loss on sale of assets	$ 297	$ (955)	197	13,618
Depreciation, depletion and amortization			4,121	9,885
Cash provided by (used in) operating activities, discontinued operations			(2,803)	16,432
Investing activities:
Oil and gas properties and equipment			(2,400)	(579)
Proceeds from sales of assets			130,146	319,351
Cash provided by (used in) investing activities, discontinued operations			200	76,236
Discontinued Operations
Operating activities:
Asset impairments			0	612
Accounts payable and other accrued liabilities			(3,000)	0
Loss on sale of assets			197	13,618
Depreciation, depletion and amortization			0	2,202
Investing activities:
Oil and gas properties and equipment			0	(579)
Proceeds from sales of assets			$ 200	$ 76,815