Schedule II - Valuation and qualifying accounts (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Tax valuation allowance
Trade receivable written-off		$ 1,400,000
Allowance for doubtful accounts
Activity in valuation and qualifying accounts
Balance at beginning of period	169,674	1,484,087	1,415,638
Additions charged to expenses	46,652	326,457	65,623
Deductions	(107,561)	(1,640,870)
Other adjustments			2,826
Balance at end of period	108,765	169,674	1,484,087
Tax valuation allowance
Trade receivable written-off		1,300,000
Deferred tax valuation allowance
Activity in valuation and qualifying accounts
Balance at beginning of period	29,416,464	29,238,264	26,452,590
Additions charged to expenses	843,479	903,463	2,845,531
Deductions	(1,784,863)	(725,263)	(59,857)
Balance at end of period	28,475,080	29,416,464	29,238,264
Tax valuation allowance
Valuation allowance related to net operating losses		400,000	1,100,000
Valuation allowance related to stock options and restricted stock		200,000
Increase in allowance attributable to decrease in bonus		200,000
Increase in allowance attributable to decrease in bad debt		500,000
Valuation allowance related to stock options and salaries and bonuses			700,000
Valuation allowance related to depreciation and amortization			$ 1,000,000