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Investments (Narrative) (Details) (USD $) |  |  | 12 Months Ended |
--- | --- | --- | --- | ---
Dec. 31, 2011 | Dec. 25, 2010 | Dec. 25, 2010 Bond Portfolio [Member] | Dec. 31, 2011 Current Investments [Member] | Dec. 31, 2011 Non-Current Investments [Member] | Dec. 31, 2011 Guarantee Payment Of Insurance Claims [Member]
Schedule of Available-for-sale Securities [Line Items] |  |  |  |  |  |
Investments, maximum maturity period, years |  |  | 5 |  |  |
Unrealized gains on the investments | $ 786,000 | $ 760,000 |  |  |  |
Investments providing collateral for letters of credit to guarantee insurance claims |  |  |  | 27,944,000 | 22,239,000 |
Letters of credit issued |  |  |  |  |  | $ 45,165,000

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