Stockholder's Equity (Summary Of Stock Option Plan Activity) (Details) - $ / shares	12 Months Ended			104 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2018
Options Outstanding
Granted (in shares)				6,382,417
Outstanding as of End of Period (in shares)	3,999,632			3,999,632
Exercisable (in shares)	1,554,378			1,554,378
Stock Option Plan
Options Outstanding
Outstanding as of Beginning of Period (in shares)	3,948,908	3,757,947
Granted (in shares)	543,968	764,789
Exercised (in shares)	(310,383)	(329,612)
Cancelled/forfeited (in shares)	(182,861)	(244,216)
Outstanding as of End of Period (in shares)	3,999,632	3,948,908	3,757,947	3,999,632
Exercisable (in shares)	1,554,378	1,280,499		1,554,378
Exercise Price
Outstanding as of Beginning of Period (in dollars per share)	$ 48.28	$ 46.81
Granted (in dollars per share)	55.00	47.00
Exercised (in dollars per share)	43.31	28.59
Cancelled/forfeited (in dollars per share)	48.86	48.22
Outstanding as of End of Period (in dollars per share)	49.53	48.28	$ 46.81	$ 49.53
Exercisable (in dollars per share)	$ 51.06	$ 50.07		$ 51.06
Remaining Life
Outstanding	5 years 7 months 9 days	5 years 10 months 20 days	5 years 10 months 6 days
Granted	9 years	9 years
Exercisable	3 years 8 months 8 days	3 years 9 months 10 days