Income Taxes (Schedule Of Effective Income Tax Rate Reconciliation) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Expense (Benefit), Continuing Operations, Income Tax Reconciliation [Abstract]
Computed expected tax expense (benefit)	$ (385,119)	$ (720,923)	$ 154,766
Increase (decrease) resulting from State and foreign income taxes	(8,038)	(6,353)	8,467
Increase (decrease) resulting other	10,431	10,861	(1,834)
Income Tax Expense (Benefit)	(267,001)	(252,020)	$ 161,399
Effective Income Tax Rate Reconciliation, Nondeductible Expense, Impairment Losses, Amount	$ 115,725	$ 464,395