Marketable Securities (Amortized Cost And Fair Value Of Marketable Securities) (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2015 USD ($)
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 208,497
Gross Unrealized Gains	53
Gross Unrealized Losses	(151)
Fair Value	208,399
Marketable securities have been in a continuous unrealized loss position for more than twelve months	0
Marketable securities that we consider to be other-than-temporarily impaired	0
Corporate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	171,949
Gross Unrealized Gains	39
Gross Unrealized Losses	(150)
Fair Value	171,838
Agency Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	18,108
Gross Unrealized Gains	3
Fair Value	18,111
U.S. Government Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	10,174
Gross Unrealized Gains	6
Fair Value	10,180
Certificates Of Deposit [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	3,400
Fair Value	3,400
Commercial Paper - Marketable Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,999
Fair Value	1,999
International Government Bond [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,467
Gross Unrealized Losses	(1)
Fair Value	1,466
Municipal Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,400
Gross Unrealized Gains	5
Fair Value	$ 1,405