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Discontinued Operations (Summarized Results from Discontinued Operations) (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Discontinued Operations and Disposal Groups [Abstract]
Revenues									$ 5,862	$ 43,845	$ 68,610
Cost of oil and gas producing activities									(6,578)	(221,402)	(94,581)
Other operating expenses									(7,754)	(10,363)	(14,357)
Loss from discontinued operations before income taxes									(8,470)	(187,920)	(40,328)
Gain (loss) on sale of assets before income taxes									(13,664)	(706)	8,526
Income tax benefit									5,269	2,496	12,193
Net income (loss) from discontinued operations available for diluted earnings per share	$ 563	$ (7,164)	$ (2,048)	$ (8,216)	$ (39,482)	$ (106,937)	$ (36,992)	$ (2,719)	$ (16,865)	$ (186,130)	$ (19,609)