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Marketable Securities - Additional Information (Detail) (USD $)
Mar. 31, 2013
Schedule of Available-for-sale Securities [Line Items]  
Unrealized losses of available-for-sale securities fair value $ 52,100,000
Aggregate fair value of available-for-sales securities in a continuous loss position greater than 12 months 1,300,000
Aggregate unrealized loss of available-for-sales securities in a continuous loss position greater than 12 months $ 26,000