Schedule II - Valuation and Qualifying Accounts - Schedule II Valuation and Qualifying Accounts (Details) - Allowance for Doubtful Accounts [Member] - USD ($)		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Balance at beginning of period		$ 1,051,424	$ 1,110,020	$ 629,457
Charged to costs and expenses		43,350	43,215	480,563
Deductions	[1]		101,811
End of period balance		$ 1,094,774	$ 1,051,424	$ 1,110,020

[1] To write-off uncollectible receivables from the allowance for royalty receivable account.