Income Taxes (Schedule Of Components Of Income Tax Expense (Benefit)) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Current, Federal									$ 19,287	$ 8,003	$ 22,914
Deferred, Federal									56,171	102,031	81,267
Total, Federal									75,458	110,034	104,181
Current, State									10,015	9,106	1,708
Deferred, State									10,463	13,619	18,699
State, Total									20,478	22,725	20,407
Current income tax expense (benefit)									29,302	17,109	24,622
Deferred income tax expense									66,634	115,650	99,966
Income tax expense (benefit)	$ 3,486	$ 34,182	$ 31,707	$ 26,561	$ 40,502	$ 34,515	$ 30,470	$ 27,272	$ 95,936	$ 132,759	$ 124,588