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Marketable Securities (Schedule Of Marketable Securities) (Details) (USD $)
In Thousands, unless otherwise specified
Dec. 31, 2011
Dec. 31, 2010
Schedule of Available-for-sale Securities [Line Items]    
Amortized cost less than one year $ 639,923 $ 534,940
Gross unrealized gains less than one year 3,901 2,973
Gross unrealized losses less than one year (285) (195)
Fair value less than one year 643,539 537,718
Amortized cost, over one year through five years 1,506,728 1,307,735
Gross unrealized gains, over one year through five years 17,075 20,084
Gross unrealized losses, over one year through five years (3,938) (2,368)
Fair value, over one year through five years 1,519,865 1,325,451
Government And Corporate Debentures - Fixed Interest Rate [Member]
    
Schedule of Available-for-sale Securities [Line Items]    
Amortized cost less than one year 504,749 313,939
Gross unrealized gains less than one year 3,534 2,372
Gross unrealized losses less than one year (237) (85)
Fair value less than one year 508,046 316,226
Amortized cost, over one year through five years 1,103,254 990,454
Gross unrealized gains, over one year through five years 14,854 18,421
Gross unrealized losses, over one year through five years (2,058) (1,731)
Fair value, over one year through five years 1,116,050 1,007,144
Government-Sponsored Enterprises [Member]
    
Schedule of Available-for-sale Securities [Line Items]    
Amortized cost less than one year 40,088 142,496
Gross unrealized gains less than one year 238 504
Gross unrealized losses less than one year   (100)
Fair value less than one year 40,326 142,900
Amortized cost, over one year through five years 295,235 189,085
Gross unrealized gains, over one year through five years 2,061 1,366
Gross unrealized losses, over one year through five years (151) (552)
Fair value, over one year through five years 297,145 189,899
Government And Corporate Debentures - Floating Interest Rate [Member]
    
Schedule of Available-for-sale Securities [Line Items]    
Amortized cost less than one year 95,086 78,505
Gross unrealized gains less than one year 129 97
Gross unrealized losses less than one year (48) (10)
Fair value less than one year 95,167 78,592
Amortized cost, over one year through five years 102,161 120,206
Gross unrealized gains, over one year through five years 160 297
Gross unrealized losses, over one year through five years (1,729) (85)
Fair value, over one year through five years 100,592 120,418
Auction Rate Securities [Member]
    
Schedule of Available-for-sale Securities [Line Items]    
Amortized cost, over one year through five years 6,078 [1] 7,990 [1]
Fair value, over one year through five years $ 6,078 [1] $ 7,990 [1]
[1] The balance in 2010 was comprised of four auction rate securities, which have suffered from failed auctions since September 2007. During 2011 two of these securities were sold. As a result of the auction failures these auction rate securities do not have a readily determinable market value. As such, since 2008, the Company determines the fair values of these securities with the assistance of third- party valuating specialists (see Note 5).