Schedule II - Valuation and Qualifying Accounts (Details) - USD ($)		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Valuation and Qualifying Accounts [Roll Forward]
Balance at beginning of period		$ 3,694,080	$ 4,748,657	$ 4,969,711
Charged to costs and expenses		1,195,500	595,500	1,898,300
Charged to other accounts		19,500	25,500	15,092
Net accounts written off	[1]	(1,465,784)	(1,675,577)	(2,134,446)
Balance at end of period		$ 3,443,296	$ 3,694,080	$ 4,748,657

[1] Net of recovery of amounts previously written off.