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Marketable Securities And Fair Value Disclosures (Summary Of Marketable Securities) (Details) (USD $)
In Thousands, unless otherwise specified
Mar. 31, 2012
Mar. 31, 2011
Short-Term Government-Backed Securities [Member]
   
Schedule of Available-for-sale Securities [Line Items]    
Cost   $ 76,368
Gross Unrealized Gains   21
Gross Unrealized Losses   (18)
Fair Market Value   76,371
Short-Term Commercial Paper [Member]
   
Schedule of Available-for-sale Securities [Line Items]    
Cost 5,276 39,728
Gross Unrealized Gains 28 45
Gross Unrealized Losses   (18)
Fair Market Value $ 5,304 $ 39,755