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Summary of Marketable Securities Treated as Available-for-Sale Securities (Detail) (USD $)
In Thousands, unless otherwise specified
Jun. 30, 2012
Dec. 31, 2011
Jun. 30, 2011
Schedule of Available-for-sale Securities [Line Items]      
Total available-for-sale securities, Amortized cost $ 27,059 $ 27,048 $ 26,048
Total available-for-sale securities, Gross unrealized gains 113 123 195
Total available-for-sale securities, Gross unrealized losses (6) (6) 0
Total available-for-sale securities, Fair value 27,166 27,165 26,243
Common stock
     
Schedule of Available-for-sale Securities [Line Items]      
Total available-for-sale securities, Amortized cost 197 197 198
Total available-for-sale securities, Gross unrealized gains 113 123 146
Total available-for-sale securities, Gross unrealized losses 0 0 0
Total available-for-sale securities, Fair value 310 320 344
Government and agency securities
     
Schedule of Available-for-sale Securities [Line Items]      
Total available-for-sale securities, Amortized cost 26,862 26,851 25,850
Total available-for-sale securities, Gross unrealized gains 0 0 49
Total available-for-sale securities, Gross unrealized losses (6) (6) 0
Total available-for-sale securities, Fair value $ 26,856 $ 26,845 $ 25,899