SCHEDULE II - Valuation and Qualifying Accounts (Details) (Allowance for doubtful accounts, USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Allowance for doubtful accounts
Valuation and Qualifying Accounts
Balance at Beginning of Period	$ 448,119	$ 482,518	$ 475,684
Additions, Charged to Costs and Expenses	190,032	265,807	374,597
Deductions	257,443	300,206	367,763
Balance at end of Period	$ 380,708	$ 448,119	$ 482,518