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Significant Accounting Policies (Details 6) (USD $)
6 Months Ended
Jun. 30, 2013
Jun. 30, 2012
Employee Stock Options:
   
Weighted-average assumptions    
Risk-free interest rate (as a percent) 1.00% 0.80%
Dividend yield (as a percent) 0.00% 0.00%
Volatility (as a percent) 51.50% 51.10%
Expected life 5 years 1 month 6 days 5 years 1 month 6 days
ESPP:
   
Weighted-average assumptions    
Risk-free interest rate (as a percent) 0.10% 0.10%
Dividend yield (as a percent) 0.00% 0.00%
Volatility (as a percent) 61.40% 42.30%
Expected life 6 months 6 months
RSUs
   
Weighted-average assumptions    
Vesting period 4 years  
RSUs | Employees
   
Weighted-average assumptions    
Weighted-average grant date fair value (in dollars per share) $ 14.48 $ 7.60
Board of Director Stock Options:
   
Weighted-average assumptions    
Risk-free interest rate (as a percent) 2.30%  
Dividend yield (as a percent) 0.00%  
Volatility (as a percent) 52.40%  
Expected life 7 years 3 months 18 days