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Estimates Weighted-average Fair Value Per Share of Options Granted (Detail)
6 Months Ended 9 Months Ended 12 Months Ended
Dec. 31, 2011
Dec. 31, 2010
Sep. 30, 2012
Sep. 30, 2011
Jun. 30, 2011
Jun. 30, 2010
Jun. 30, 2009
Share Based Compensation [Line Items]              
Expected volatility, minimum 56.00% 57.00% 54.00% 50.00% 50.00%   69.00%
Expected volatility, maximum 69.00% 67.00% 57.00% 69.00% 69.00% 65.00% 75.00%
Expected term (in years) 5 years 9 months 6 years 15 days 6 years 18 days 5 years 9 months 29 days 6 years 18 days 6 years 7 days 5 years 7 months 13 days
Risk-free interest rate, minimum 0.00% 1.43% 0.87% 0.00% 1.43% 2.57% 1.48%
Risk-free interest rate, maximum 1.92% 2.96% 1.18% 3.03% 2.96% 3.04% 3.77%
Dividend yield 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%
Employee Stock Purchase Plan
             
Share Based Compensation [Line Items]              
Expected volatility     42.00%        
Expected term (in years)     1 month 28 days        
Risk-free interest rate     0.16%