Marketable Securities (Amortized Cost And Fair Value Of Marketable Securities) (Details) - USD ($) $ in Thousands	6 Months Ended
Jun. 30, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 228,880	$ 213,804
Gross Unrealized Gains	228	25
Gross Unrealized Losses	(45)	(238)
Fair Value	229,063	213,591
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	144,591	177,810
Gross Unrealized Gains	131	24
Gross Unrealized Losses	(45)	(221)
Fair Value	144,677	177,613
Asset-backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	28,263
Gross Unrealized Gains	70
Fair Value	28,333
Certificates Of Deposit [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	20,800	3,500
Fair Value	20,800	3,500
Commercial Paper - Marketable Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	18,224	3,491
Fair Value	18,224	3,491
U.S. Government Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	12,601	12,881
Gross Unrealized Gains	21
Gross Unrealized Losses		(10)
Fair Value	12,622	12,871
Agency Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	2,400	12,068
Gross Unrealized Gains	1
Gross Unrealized Losses		(3)
Fair Value	2,401	12,065
Municipal Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,400	1,400
Gross Unrealized Gains	5
Gross Unrealized Losses		(1)
Fair Value	1,405	1,399
International Government Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	601	1,462
Gross Unrealized Losses		(3)
Fair Value	$ 601	1,459
Treasury Bills [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		1,192
Gross Unrealized Gains		1
Fair Value		$ 1,193

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 25
-Paragraph 1
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Reference 2: http://www.xbrl.org/2003/role/presentationRef
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