Schedule II - Valuation and Qualifying Accounts (Details) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Valuation and Qualifying Accounts [Roll Forward]
Balance at beginning of period	$ 4,748,657	$ 4,969,711	$ 4,816,118
Charged to costs and expenses	595,500	1,898,300	2,373,342
Charged to other accounts	25,500	15,092	37,200
Net accounts written off	(1,675,577)	(2,134,446)	(2,256,949)
Balance at end of period	$ 3,694,080	$ 4,748,657	$ 4,969,711