Commitments and contingencies (Details Textual) - USD ($)	1 Months Ended	6 Months Ended
	Mar. 20, 2015	Jun. 30, 2015	Jun. 30, 2014
Operating Leased Assets [Line Items]
Operating Leases, Rent Expense, Net		$ 380,641	$ 443,713
Fifth Amendment To Lease Agreement Of Corporate Facility
Operating Leased Assets [Line Items]
Lessee Leasing Arrangements, Operating Leases, Term of Contract	69 months
Lessee Leasing Arrangements, Operating Leases, Renewal Term	5 years
Fifth Amendment To Lease Agreement Of Corporate Facility | Maximum
Operating Leased Assets [Line Items]
Lessee Leasing Arrangements Operating Leases Option Term	1 year