Independent Directors' Stock Option (Details) (Independent director's stock option plan, USD $)
6 Months Ended
Jun. 30, 2012
Dec. 31, 2009
Dec. 31, 2008
Dec. 31, 2007
Dec. 31, 2006
Dec. 31, 2005
Independent director's stock option plan
           
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Stock options granted, expected term 10 years          
Stock options granted, excercise price   $ 9.10 $ 9.10 $ 9.10 $ 9.15 $ 9.15
Stock options, exercise price of future options 100.00%          
Stock options, shares to purchase 50,000          
Stock options, outstanding 45,000          
Stock options, wieghted average contractual remaining life 5 years          
Stock options granted, weighted average exercise price $ 9.12          
Number of shares authorized 1,000,000          
Number of shares reserved for issuance under the IDSOP 1,000,000