QUALIFYING ACCOUNTS (Details) - Allowance for doubtful accounts - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Valuation and Qualifying Accounts
Balance at Beginning of Period	$ 643,990	$ 523,004	$ 372,828
Additions, Charged to Costs and Expenses	357,789	422,109	365,746
Deductions	469,618	301,123	215,570
Balance at end of Period	$ 532,161	$ 643,990	$ 523,004