Income Taxes (Schedule Of Effective Income Tax Rate Reconciliation) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Income Tax Disclosure [Abstract]
Income (loss) before income taxes	$ 40,021	$ (311,274)
Income tax (expense) benefit at the statutory rate	(14,007)	108,946
State income tax (expense) benefit, net of U.S. federal income taxes	(710)	1,619
Tax shortfalls from stock-based compensation expense	(2,592)	0
Deferred tax assets valuation allowance	17,369	(110,679)
Other	(60)	(7)
Income tax (expense) benefit	$ 0	$ (121)