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, 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
Earnings Per Share [Abstract]
Income (loss) of basic earnings (loss) per common share	$ 1,683		$ (24,022)		$ (72,136)		$ (41,149)		$ (309,337)	$ (205,281)	$ (274,389)	$ (248,354)	$ (135,624)	$ (1,037,361)	$ 136,276
Income (loss) of effect of dilutive stock options, restricted stock, and SARs													0	0	0
Income (loss) of diluted earnings (loss) per common share													$ (135,624)	$ (1,037,361)	$ 136,276
Weighted shares of basic earnings (loss) per common share													50,029	49,110	48,611
Weighted shares of effect of dilutive stock options, restricted stock, and SARs													0	0	472
Weighted shares of diluted earnings (loss) per common share													50,029	49,110	49,083
Per share amount of basic earnings (loss) per common share	$ 0.03		$ (0.48)		$ (1.44)		$ (0.83)		$ (6.29)	$ (4.18)	$ (5.58)	$ (5.07)	$ (2.71)	$ (21.12)	$ 2.80
Per share amount of effect of dilutive stock options, restricted stock, and SARs													0.00	0.00	(0.02)
Per share amount of diluted earnings (loss) per common share	$ 0.03	[1]	$ (0.48)	[1]	$ (1.44)	[1]	$ (0.83)	[1]	$ (6.29)	$ (4.18)	$ (5.58)	$ (5.07)	$ (2.71)	$ (21.12)	$ 2.78

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