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Financial Instruments - Investments from Continuing Operations (Detail) (USD $)
In Thousands, unless otherwise specified
Mar. 31, 2013
Mar. 30, 2013
Dec. 31, 2012
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]      
Total investments (available for sale), Cost   $ 71,802 $ 71,729
Short-term investments (available-for-sale), Gross Unrealized, Gain 4   4
Short-term investments (available-for-sale), Gross Unrealized (Loss) (473)   (475)
Short-term investments (available-for-sale), Fair value 71,333   71,258
U.S. Treasury bills [Member]
     
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]      
Short-term investments (available-for-sale), Cost   63,952 63,879
Short-term investments (available-for-sale), Gross Unrealized, Gain 4   4
Short-term investments (available-for-sale), Gross Unrealized (Loss) (5)   (7)
Short-term investments (available-for-sale), Fair value 63,951   63,876
Municipal bond [Member]
     
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]      
Long-term investments (available-for-sale), Cost   7,850 7,850
Long-term investments (available-for-sale), Gross Unrealized, Gain        
Long-term investments (available-for-sale), Gross Unrealized (Loss) (468)   (468)
Short-term investments (available-for-sale), Fair value 7,382   7,382
Long-term investments (available-for-sale), Fair value $ 7,382   $ 7,382