Schedule II - Valuation and Qualifying Accounts (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Valuation and Qualifying Accounts [Roll Forward]
Balance at beginning of period	$ 4,969,711	$ 4,816,118	$ 4,100,333
Charged to costs and expenses	1,898,300	2,373,342	2,825,300
Charged to other accounts	15,092	37,200	44,400
Net accounts written off	(2,134,446)	(2,256,949)	(2,153,915)
Balance at end of period	$ 4,748,657	$ 4,969,711	$ 4,816,118