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Marketable Securities (Detail) (USD $)
In Thousands, unless otherwise specified
3 Months Ended 9 Months Ended 15 Months Ended
Sep. 30, 2012
Sep. 30, 2012
Sep. 30, 2011
Sep. 30, 2012
Marketable Securities [Abstract]        
Investment Income, Amortization of Premium $ 182 $ 710 $ 898 $ 234