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Share-Based Payments (Details 3) (USD $)
12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Share-based payments, additional disclosure      
Stock-based compensation recognized $ 339,000 $ (82,000) $ 297,000
Research and development
     
Share-based payments, additional disclosure      
Stock-based compensation recognized 208,000 63,000 53,000
Selling, general and administrative
     
Share-based payments, additional disclosure      
Stock-based compensation recognized 131,000 (145,000) 244,000
Stock option
     
Assumptions used in estimating the fair value of each option award using the Black-Scholes option-pricing model      
Expected volatility, minimum (as a percent) 68.30% 59.10% 60.30%
Expected volatility, maximum (as a percent) 71.60% 74.70% 61.50%
Dividend Yield (as a percent) 0.00% 0.00% 0.00%
Expected term 6 years 3 months   6 years 3 months
Risk-free rate, minimum (as a percent) 0.89% 0.15% 1.65%
Risk-free rate, maximum (as a percent) 1.14% 2.93% 2.72%
Expected forfeiture rate (as a percent)     5.00%
Number of Options      
Outstanding at the beginning of the period (in shares) 598,109 664,479  
Granted (in shares) 188,136 144,750  
Exercised (in shares) (159,264) (69,599)  
Forfeited or expired (in shares) (57,070) (141,561)  
Outstanding at the end of the period (in shares) 569,911 598,109 664,479
Vested and expected to vest (in shares) 564,083    
Exercisable (in shares) 200,312    
Weighted-Average Exercise Price      
Outstanding at the beginning of the period (in dollars per share) $ 2.75 $ 1.72  
Granted (in dollars per share) $ 10.73 $ 5.80  
Exercised (in dollars per share) $ 1.67 $ 0.40  
Forfeited or expired (in dollars per share) $ 2.45 $ 2.17  
Outstanding at the end of the period (in dollars per share) $ 5.72 $ 2.75 $ 1.72
Vested and expected to vest (in dollars per share) $ 5.72    
Exercisable (in dollars per share) $ 2.11    
Weighted-Average Remaining Contractual Term      
Outstanding at the end of the period 7 years 10 months 17 days 7 years 8 months 16 days 7 years 9 months 29 days
Vested and expected to vest 7 years 10 months 13 days    
Exercisable 5 years 8 months 23 days    
Share-based payments, additional disclosure      
Aggregate intrinsic value of options outstanding 1,600,000 1,900,000 589,000
Aggregate intrinsic value of options vested and expected to vest 1,500,000 1,800,000 585,000
Aggregate intrinsic value of options exercisable 1,000,000 1,200,000 463,000
Weighted-average, grant-date fair value of options granted (in dollars per share) $ 6.85 $ 3.64 $ 1.68
Total fair value of the common stock vested 218,000 113,000 104,000
Total intrinsic value of options exercised 748,000 262,000 26,000
Total unrecognized compensation expense, net of related forfeiture estimates 1,651,000 768,000  
Weighted-average period over which total unrecognized compensation expense is expected to be recognized 3 years 22 days 3 years 1 month 2 days  
Stock option | Minimum
     
Assumptions used in estimating the fair value of each option award using the Black-Scholes option-pricing model      
Fair value of common stock (in dollars per share) $ 5.07 $ 2.56 $ 1.60
Expected term   4 months 28 days  
Expected forfeiture rate (as a percent) 0.00% 0.00%  
Stock option | Maximum
     
Assumptions used in estimating the fair value of each option award using the Black-Scholes option-pricing model      
Fair value of common stock (in dollars per share) $ 12.92 $ 3.36 $ 7.04
Expected term   6 years 3 months  
Expected forfeiture rate (as a percent) 5.00% 5.00%  
ESPP
     
Share-based payments, additional disclosure      
Purchase price expressed as a percentage of fair market value of common stock 85.00%    
Common stock purchased by eligible employees (in shares) 36,727    
Stock-based compensation recognized 104,000    
Common Stock reserved for future employee purchase (in shares) 213,273    
ESPP | Research and development
     
Share-based payments, additional disclosure      
Stock-based compensation recognized 55,000    
ESPP | Selling, general and administrative
     
Share-based payments, additional disclosure      
Stock-based compensation recognized $ 49,000