Long and short-term capital leases (Details) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Long and short-term capital leases
Less: short-term portion capital leases	$ (290,911)	$ (458,812)
Capital leases to various lessors secured by financed equipment with interest rates ranging from 4.67% to 13.45%.
Long and short-term capital leases
Capital leases to various lessors secured by financed equipment with interest rates ranging from 4.67% to 13.45%. Principal and interest are payable monthly through September 2018	487,111	816,718
Total long and short-term portions of capital leases	487,111	816,718
Less: short-term portion capital leases	(290,911)	(458,812)
Long-term portion of capital leases	196,200	357,906
Total term debt interest expense	$ 46,958	$ 61,591	$ 60,106
Capital leases to various lessors secured by financed equipment with interest rates ranging from 4.67% to 13.45%. | Minimum
Long and short-term capital leases
Interest rate (as a percent)	4.67%
Capital leases to various lessors secured by financed equipment with interest rates ranging from 4.67% to 13.45%. | Maximum
Long and short-term capital leases
Interest rate (as a percent)	13.45%