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Stockholders' Equity (Details 1) (USD $)
 12 Months Ended
Dec. 31, 2011
Dec. 31, 2010
Dec. 31, 2009
Qualified Stock Option Plans [Member]
      
Stock option activities of qualified stock option plans      
Stock option outstanding at beginning of year, shares 389,026    
Number of shares of stock options granted 249,000    
Exercise of stock options, shares (114,996)    
Stock option cancelled, forfeited or expired, shares (6,700)    
Stock option, outstanding at end of year, shares 516,330 389,026  
Stock option exercisable at end of year, shares 89,065    
Stock option outstanding at beginning of year, weighted-average exercise price $ 8.41    
Stock option granted, weighted-average exercise price $ 34.41    
Stock option exercised, weighted-average exercise price $ 6.54    
Stock option cancelled, forfeited or expired, weighted-average exercise price $ 9.69    
Stock option, outstanding at end of year, weighted-average exercise price $ 21.34 $ 8.41  
Stock option exercisable at end of year, weighted-average exercise price $ 8.85    
Weighted-average fair value per options granted during year $ 16.00    
Total intrinsic value of options exercised during the year $ 3,294,000 $ 441,000 $ 3,051,000
Total fair value of options vested during the year 208,000 214,000 220,000
Non-Qualified Stock Option Plans [Member]
      
Stock option activities of qualified stock option plans      
Stock option outstanding at beginning of year, shares 374,600    
Number of shares of stock options granted 5,000    
Exercise of stock options, shares (63,075)    
Stock option cancelled, forfeited or expired, shares 0    
Stock option, outstanding at end of year, shares 316,525 374,600  
Stock option exercisable at end of year, shares 66,325    
Stock option outstanding at beginning of year, weighted-average exercise price $ 7.83    
Stock option granted, weighted-average exercise price $ 34.50    
Stock option exercised, weighted-average exercise price $ 7.05    
Stock option cancelled, forfeited or expired, weighted-average exercise price $ 0.00    
Stock option, outstanding at end of year, weighted-average exercise price $ 8.41 $ 7.83  
Stock option exercisable at end of year, weighted-average exercise price $ 7.97    
Weighted-average fair value per options granted during year $ 16.25    
Total intrinsic value of options exercised during the year 2,110,000 805,000 2,201,000
Total fair value of options vested during the year $ 730,000 $ 721,000 $ 721,000