ACCOUNTS RECEIVABLE (Tables)
 12 Months Ended
Dec. 31, 2013
ACCOUNTS RECEIVABLE [Abstract]  
Schedule of Accounts Receivable

Accounts receivable consists of the following:

 

    December 31,  
    2012     2013  
Accounts receivable     129,476,266       170,347,528  
Allowance for doubtful accounts     (1,503,621 )     (2,254,797 )
Accounts receivable, net     127,972,645       168,092,731  

 
Schedule of Allowance for Doubtful Accounts

The following table presents movement of the allowance for doubtful accounts:

 

    December 31,  
    2011     2012     2013  
Balance at the beginning of year     304,796       1,323,490       1,503,621  
Additions     1,576,739       1,137,574       2,650,128  
Write-offs     (558,045 )     (957,443 )     (1,898,952 )
Balance at the end of year     1,323,490       1,503,621       2,254,797