STATEMENTS OF COMPREHENSIVE INCOME (Parenthetical) - USD ($)
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
STATEMENTS OF COMPREHENSIVE INCOME      
Change in fair value of available-for-sale securities, tax benefit $ 19,406 $ 23,500 $ 10,659
Reclassification to net income, tax (benefit) expense $ (30,757) $ (1,334) $ 2,560