Consolidated Statement of Stockholders' Equity (Unaudited) - 9 months ended Sep. 30, 2016 - USD ($)
Total
Common Stock
Additional Paid-In Capital
Treasury Stock
Retained Earnings
Balance at beginning of period (in shares) at Dec. 31, 2015   29,765,525      
Balance at beginning of period at Dec. 31, 2015 $ 395,249,574 $ 2,979 $ 319,002,254 $ (784,829) $ 77,029,170
Treasury stock at beginning of period (in shares) at Dec. 31, 2015 (37,937)     (37,937)  
Increase (decrease) in stockholders' equity:          
Share compensation expense $ 11,158,738   11,158,738    
Exercise of stock options (in shares)   132,968      
Exercise of stock options 754,739 $ 13 754,726    
Common stock issued for vested restricted stock (in shares)   618,154      
Common stock issued for vested restricted stock 0 $ 62 (62)    
Common stock issued for vested performance shares (in shares)   37,547      
Common stock issued for vested performance shares 0 $ 4 (4)    
Common shares withheld and retired to satisfy employee tax withholding obligations upon vesting of share-based awards (in shares)   (202,715)      
Common shares withheld and retired to satisfy employee tax withholding obligations upon vesting of share-based awards (4,679,014) $ (20) (4,678,994)    
Tax deficiency from exercise of stock options (231,521)   (231,521)    
Purchases of treasury stock (in shares)       (1,678,345)  
Purchases of treasury stock (35,686,243)     $ (35,686,243)  
Net income 4,555,430       4,555,430
Balance at end of period (in shares) at Sep. 30, 2016   30,351,479      
Balance at end of period at Sep. 30, 2016 $ 371,121,703 $ 3,038 $ 326,005,137 $ (36,471,072) $ 81,584,600
Treasury stock at end of period (in shares) at Sep. 30, 2016 (1,716,282)     (1,716,282)