Schedule II - Valuation and Qualifying Accounts (Details) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Valuation and qualifying accounts [Roll Forward]
Balance at beginning of period	$ 4,588,675	$ 4,242,335	$ 4,275,899
Charged to costs and expenses	2,174,729	2,805,311	3,409,313
Charged to other accounts	49,500	49,500	48,946
Net accounts written off	(2,712,571)	(2,508,471)	(3,491,823)
Balance at end of period	$ 4,100,333	$ 4,588,675	$ 4,242,335