Annual report pursuant to Section 13 and 15(d)

Consolidated Statements of Changes in Stockholders' Equity (Parenthetical)

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Consolidated Statements of Changes in Stockholders' Equity (Parenthetical) (USD $)
12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Statement of Stockholders' Equity [Abstract]      
Stock-based compensation expense, excess tax benefits $ 259,890 $ 2,725,533 $ 2,010,221