Stockholder's Equity (Summary Of Stock Option Plan Activity) (Details) - $ / shares	12 Months Ended			104 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2017
Options Outstanding
Granted (in shares)				6,628,449
Outstanding as of End of Period (in shares)	3,948,908			3,948,908
Exercisable (in shares)	1,280,499			1,280,499
Stock Option Plan [Member]
Options Outstanding
Outstanding as of Beginning of Period (in shares)	3,757,947	4,530,982
Granted (in shares)	764,789	845,440
Exercised (in shares)	(329,612)	(1,180,242)
Cancelled/Forfeited (in shares)	(244,216)	(438,233)
Outstanding as of End of Period (in shares)	3,948,908	3,757,947	4,530,982	3,948,908
Exercisable (in shares)	1,280,499	1,200,250		1,280,499
Exercise Price
Outstanding as of Beginning of Period (in dollars per share)	$ 46.81	$ 41.49
Granted (in dollars per share)	47.00	46.00
Exercised (in dollars per share)	28.59	24.80
Cancelled/Forfeited (in dollars per share)	48.22	49.49
Outstanding as of End of Period (in dollars per share)	48.28	46.81	$ 41.49	$ 48.28
Exercisable (in dollars per share)	$ 50.07	$ 45.93		$ 50.07
Remaining Life
Outstanding	5 years 10 months 20 days	5 years 10 months 6 days	4 years 10 months 20 days
Granted	9 years	8 years 4 months 27 days
Exercisable	3 years 9 months 10 days	3 years 8 months 26 days