Marketable Securities (Amortized Cost And Fair Value Of Marketable Securities) (Details) $ in Thousands	12 Months Ended
Dec. 31, 2015 USD ($)
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 213,804
Gross Unrealized Gains	25
Gross Unrealized Losses	(238)
Fair Value	213,591
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	177,810
Gross Unrealized Gains	24
Gross Unrealized Losses	(221)
Fair Value	177,613
U S Government Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	12,881
Gross Unrealized Losses	(10)
Fair Value	12,871
Agency Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	12,068
Gross Unrealized Losses	(3)
Fair Value	12,065
Certificates Of Deposit [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	3,500
Fair Value	3,500
Markerable Securities - Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	3,491
Fair Value	3,491
International Government Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,462
Gross Unrealized Losses	(3)
Fair Value	1,459
Municipal Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,400
Gross Unrealized Losses	(1)
Fair Value	1,399
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.

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