Earnings Per Share (Schedule Of Earnings (Loss) Per Share) (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
Earnings Per Share [Abstract]
Income (loss) of basic earnings (loss) per common share	$ (309,337)	$ (205,281)	$ (274,389)	$ (248,354)	$ (42,551)		$ 67,522		$ 54,360		$ 56,945		$ (1,037,361)	$ 136,276	$ 184,746
Income (loss) of effect of dilutive stock options, restricted stock, and SARs													0	0	0
Income (loss) of diluted earnings (loss) per common share													$ (1,037,361)	$ 136,276	$ 184,746
Weighted shares of basic earnings (loss) per common share													49,110	48,611	48,218
Weighted shares of effect of dilutive stock options, restricted stock, and SARs													0	472	354
Weighted shares of diluted earnings (loss) per common share													49,110	49,083	48,572
Per share amount of basic earnings (loss) per common share	$ (6.29)	$ (4.18)	$ (5.58)	$ (5.07)	$ (0.88)		$ 1.39		$ 1.12		$ 1.17		$ (21.12)	$ 2.80	$ 3.83
Per share amount of effect of dilutive stock options, restricted stock, and SARs													0.00	(0.02)	(0.03)
Per share amount of diluted earnings (loss) per common share	$ (6.29)	$ (4.18)	$ (5.58)	$ (5.07)	$ (0.88)	[1]	$ 1.37	[1]	$ 1.11	[1]	$ 1.17	[1]	$ (21.12)	$ 2.78	$ 3.80

[1] Due to the effect of the loss in the fourth quarter, the diluted earnings per share for the year's four quarters does not equal annual earnings per share.