Income Taxes (Summary Of Provision For Income Taxes) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Income Tax Disclosure [Abstract]
Tax (benefit) expense	$ (17,264)	$ 925	$ 11,379	$ 1,286
Pretax income (loss)	$ 184,499	$ (12,408)	$ 435,189	$ (34,325)
Effective tax rates (percentage)	(9.40%)	(7.50%)	2.60%	(3.70%)