Commitments and contingencies (Details Textual) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Commitments and Contingencies Disclosure [Line Items]
Operating Leases, Rent Expense	$ 2,908,175	$ 2,540,031
Investment Company, Committed Capital	$ 10,971,456
Minimum [Member]
Commitments and Contingencies Disclosure [Line Items]
Lease Expiration Year	2019
Maximum [Member]
Commitments and Contingencies Disclosure [Line Items]
Lease Expiration Year	2022