Quarterly Financial Data (unaudited) (Schedule Of Quarterly Financial Information) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended												12 Months Ended
	Dec. 31, 2015		Sep. 30, 2015		Jun. 30, 2015		Mar. 31, 2015		Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Oil and natural gas revenues	$ 64,743		$ 83,526		$ 93,742		$ 86,320		$ 127,789	$ 151,042	$ 182,966	$ 198,472	$ 328,331	$ 660,269	$ 634,309
Operating income (loss)	(240,817)	[1]	(363,975)	[1]	(421,465)	[1]	(313,618)	[1]	3,341	22,799	43,312	57,423	(1,339,875)	126,875	179,221
Net income (loss)	$ (65,595)	[2]	$ (354,519)	[2]	$ (454,155)	[2]	$ (318,112)	[2]	$ 81,413	$ 41,569	$ 2,293	$ (4,606)	$ (1,192,381)	$ 120,669	$ 22,204
Net income (loss) per basic common share	$ (0.24)		$ (1.30)		$ (1.67)		$ (1.17)		$ 0.30	$ 0.15	$ 0.01	$ (0.02)	$ (4.36)	$ 0.45	$ 0.10
Weighted average shares	277,995		273,348		271,549		271,522		271,053	270,631	270,492	260,716	273,621	268,258	215,011
Net income (loss) per diluted common share	$ (0.24)		$ (1.30)		$ (1.67)		$ (1.17)		$ 0.30	$ 0.15	$ 0.01	$ (0.02)	$ (4.36)	$ 0.45	$ 0.10
Weighted average shares	277,995		273,348		271,549		271,522		271,053	272,066	271,226	260,716	273,621	268,376	230,912
Impairment of oil and natural gas properties	$ 205,300		$ 339,400		$ 394,300		$ 276,300						$ 1,215,370	$ 0	$ 108,546
Net gain on restructuring of debt	$ 193,300												$ 193,276	$ 0	$ 0

[1] Operating loss for the first, second, third and fourth quarter of 2015 includes $276.3 million, $394.3 million, $339.4 million and $205.3 million, respectively, of impairments of oil and natural gas properties. See "Note 2. Summary of significant accounting policies" for further discussion.

[2] Net loss for the fourth quarter of 2015 includes a $193.3 million net gain on restructuring and extinguishment of debt. See "Note 5. Debt" for further discussion.