Reduction in Value of Assets (Schedule Of Reduction In Value Of Assets) (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Reduction in Value of Assets [Abstract]
Reduction in value of goodwill				$ 330,500,000
Reduction in value of long-lived assets			$ 9,900,000	105,859,000
Retirements of long-lived assets				26,102,000
Total reduction in value of assets	$ 9,953,000	$ 0	$ 9,953,000	$ 462,461,000