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Available for Sale Securities by Original Contractual Maturity (Detail) (USD $)
In Thousands, unless otherwise specified
Mar. 31, 2013
Dec. 31, 2012
Carrying Value
    
Schedule of Available-for-sale Securities [Line Items]    
Due in one year or less $ 53,569 $ 10,268
Due greater than three years and less than five years 0 0
Total cash equivalents and short-term investments 53,569 10,268
Fair Value
    
Schedule of Available-for-sale Securities [Line Items]    
Due in one year or less 53,569 10,268
Due greater than three years and less than five years 0 0
Total cash equivalents and short-term investments $ 53,569 $ 10,268