Stock-based Compensation (Details Textual) (USD $)
3 Months Ended 6 Months Ended
Jun. 30, 2012
Mar. 31, 2012
Mar. 31, 2011
Jun. 30, 2012
Jun. 30, 2011
Stock-based compensation (Textual) [Abstract]          
Stock-based compensation expense   $ 0 $ 0 $ 983,000 $ 408,000
Employee stock option plans to purchase common stock, authorized 8,296,777     8,296,777  
Duration in which options vest ratable       4 years  
Employee stock option plans to purchase common stock, expiry period       10 years  
Options exercised under early exercise of option plan       0  
Weighted-average remaining contractual life of the options outstanding and expected to vest       7 years 6 months  
Total intrinsic value of options exercised 375,000     17,556,000  
Unrecognized compensation cost related to non-vested options granted 5,170,000     5,170,000  
Expected weighted average period to recognize unrecognized compensation cost       2 years 2 months 12 days  
Total fair value of shares vested 325,000     748,000  
Tax deduction allowed for incentive stock options 0        
Deferred income tax asset for the expense related to options   0      
Closing stock price as reported on the NASDAQ $ 13.70     $ 13.70