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Restructuring - Additional Information (Detail) (USD $)	1 Months Ended	3 Months Ended
Restructuring - Additional Information (Detail) (USD $)	Nov. 30, 2012 Employee	Mar. 31, 2013
Restructuring Cost and Reserve [Line Items]
Reduction in workforce, number of employees	21
Restructuring charges included severance and related costs		$ 462,000
Research and development
Restructuring Cost and Reserve [Line Items]
Restructuring charges included severance and related costs		264,000
General and administrative
Restructuring Cost and Reserve [Line Items]
Restructuring charges included severance and related costs		$ 198,000

Amount charged against earnings in the period for incurred and estimated costs associated with exit from or disposal of business activities or restructurings pursuant to a duly authorized plan, excluding asset retirement obligations.

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