Discontinued Operations (Significant Operating and Investing Activities of Discontinued Operations) (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Operating activities:
Asset impairments			$ 37,900	$ 49,438
Accounts payable and other accrued liabilities			(6,135)	(16,069)
Loss on sale of assets	$ (100)	$ 3,596	(100)	14,573
Depreciation, depletion and amortization			2,862	7,268
Cash provided by (used in) operating activities, discontinued operations			(3,000)	17,332
Investing activities:
Oil and gas properties and equipment			(2,400)	(567)
Proceeds from sales of assets			130,011	318,480
Cash provided by (used in) investing activities, discontinued operations			100	75,377
Discontinued Operations
Operating activities:
Asset impairments			0	612
Accounts payable and other accrued liabilities			(3,000)	0
Loss on sale of assets			0	14,573
Depreciation, depletion and amortization			0	2,147
Investing activities:
Oil and gas properties and equipment			0	(567)
Proceeds from sales of assets			$ 100	$ 75,944