XML 11 R39.htm IDEA: XBRL DOCUMENT v2.4.0.8
Assumptions Used to Estimate Fair Value of Employee Stock Purchase Plan (Detail) (Employee stock purchase plan)
3 Months Ended
Mar. 31, 2014
Mar. 31, 2013
Employee stock purchase plan
   
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Expected dividend yield 0.00% 0.00%
Expected volatility, Minimum 43.00% 45.00%
Expected volatility, Maximum 52.00% 53.00%
Risk-free interest rate, Minimum 0.10% 0.10%
Risk-free interest rate, Maximum 0.20% 0.20%
Expected forfeiture 0.00% 0.00%
Contractual term of up to 24 months 24 months