Long and short-term capital leases (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Long and short-term capital leases
Total long and short-term portions of capital leases	$ 701,598	$ 495,987
Less short-term portion capital leases	(337,588)	(247,257)
Long-term portion of capital leases	364,010	248,730
Total term debt interest expense	55,699	64,462	361,000
Capital leases to various lessors secured by financed equipment with interest rates ranging from [7.75% to 20.04%]
Long and short-term capital leases
Total long and short-term portions of capital leases	701,598	495,987
Less short-term portion capital leases	(337,588)	(247,257)
Long-term portion of capital leases	364,010	248,730
Total term debt interest expense	55,699	64,462	65,257
Capital leases to various lessors secured by financed equipment with interest rates ranging from [7.75% to 20.04%] | Minimum
Long and short-term capital leases
Interest rate (as a percent)	4.67%	4.67%
Capital leases to various lessors secured by financed equipment with interest rates ranging from [7.75% to 20.04%] | Maximum
Long and short-term capital leases
Interest rate (as a percent)	20.04%	20.04%
Inter-Atlantic Fund L.P. note payable (non-cash)
Long and short-term capital leases
Total term debt interest expense			$ 295,743