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Fair Value Of Financial Instruments (Schedule Of Fair Value Of Financial Assets) (Details) (USD $)
In Thousands, unless otherwise specified
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Dec. 31, 2011
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Mar. 26, 2011
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| Schedule of Trading Securities and Other Trading Assets [Line Items] |
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| Fair value of financial assets |
$ 148,676 |
$ 205,429 |
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Quoted Prices In Active Markets For Identical Assets Level 1 [Member]
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| Schedule of Trading Securities and Other Trading Assets [Line Items] |
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| Fair value of financial assets |
51,367 |
63,481 |
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Significant Other Observable Inputs Level 2 [Member]
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| Schedule of Trading Securities and Other Trading Assets [Line Items] |
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| Fair value of financial assets |
97,309 |
141,948 |
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Significant Unobservable Inputs Level 3 [Member]
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| Schedule of Trading Securities and Other Trading Assets [Line Items] |
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| Fair value of financial assets |
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Money-Market Funds [Member]
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| Schedule of Trading Securities and Other Trading Assets [Line Items] |
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| Fair value of financial assets |
27,220 |
17,700 |
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Money-Market Funds [Member] | Quoted Prices In Active Markets For Identical Assets Level 1 [Member]
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| Schedule of Trading Securities and Other Trading Assets [Line Items] |
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| Fair value of financial assets |
27,220 |
17,700 |
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Money-Market Funds [Member] | Significant Other Observable Inputs Level 2 [Member]
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| Schedule of Trading Securities and Other Trading Assets [Line Items] |
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| Fair value of financial assets |
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|
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Money-Market Funds [Member] | Significant Unobservable Inputs Level 3 [Member]
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| Schedule of Trading Securities and Other Trading Assets [Line Items] |
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| Fair value of financial assets |
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Corporate Debt Securities [Member]
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| Schedule of Trading Securities and Other Trading Assets [Line Items] |
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| Fair value of financial assets |
59,640 |
64,212 |
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Corporate Debt Securities [Member] | Quoted Prices In Active Markets For Identical Assets Level 1 [Member]
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| Schedule of Trading Securities and Other Trading Assets [Line Items] |
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| Fair value of financial assets |
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Corporate Debt Securities [Member] | Significant Other Observable Inputs Level 2 [Member]
|
|
|
| Schedule of Trading Securities and Other Trading Assets [Line Items] |
|
|
| Fair value of financial assets |
59,640 |
64,212 |
|
Corporate Debt Securities [Member] | Significant Unobservable Inputs Level 3 [Member]
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| Schedule of Trading Securities and Other Trading Assets [Line Items] |
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| Fair value of financial assets |
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U.S. Treasury Securities [Member]
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| Schedule of Trading Securities and Other Trading Assets [Line Items] |
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| Fair value of financial assets |
24,147 |
45,781 |
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U.S. Treasury Securities [Member] | Quoted Prices In Active Markets For Identical Assets Level 1 [Member]
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| Schedule of Trading Securities and Other Trading Assets [Line Items] |
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|
| Fair value of financial assets |
24,147 |
45,781 |
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U.S. Treasury Securities [Member] | Significant Other Observable Inputs Level 2 [Member]
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|
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| Schedule of Trading Securities and Other Trading Assets [Line Items] |
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| Fair value of financial assets |
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|
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U.S. Treasury Securities [Member] | Significant Unobservable Inputs Level 3 [Member]
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| Schedule of Trading Securities and Other Trading Assets [Line Items] |
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| Fair value of financial assets |
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Agency Discount Notes [Member]
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| Schedule of Trading Securities and Other Trading Assets [Line Items] |
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| Fair value of financial assets |
17,838 |
16,591 |
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Agency Discount Notes [Member] | Quoted Prices In Active Markets For Identical Assets Level 1 [Member]
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| Schedule of Trading Securities and Other Trading Assets [Line Items] |
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| Fair value of financial assets |
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Agency Discount Notes [Member] | Significant Other Observable Inputs Level 2 [Member]
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|
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| Schedule of Trading Securities and Other Trading Assets [Line Items] |
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|
| Fair value of financial assets |
17,838 |
16,591 |
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Agency Discount Notes [Member] | Significant Unobservable Inputs Level 3 [Member]
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| Schedule of Trading Securities and Other Trading Assets [Line Items] |
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| Fair value of financial assets |
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Commercial Paper [Member]
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| Schedule of Trading Securities and Other Trading Assets [Line Items] |
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| Fair value of financial assets |
19,831 |
61,145 |
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Commercial Paper [Member] | Quoted Prices In Active Markets For Identical Assets Level 1 [Member]
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| Schedule of Trading Securities and Other Trading Assets [Line Items] |
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| Fair value of financial assets |
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Commercial Paper [Member] | Significant Other Observable Inputs Level 2 [Member]
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| Schedule of Trading Securities and Other Trading Assets [Line Items] |
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| Fair value of financial assets |
19,831 |
61,145 |
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Commercial Paper [Member] | Significant Unobservable Inputs Level 3 [Member]
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| Schedule of Trading Securities and Other Trading Assets [Line Items] |
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| Fair value of financial assets |
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