Commitments and contingencies - Capital leases (Details) - USD ($)	Dec. 31, 2016	Dec. 31, 2015
Analysis of the leased property under capital leases
Total capital leases, gross	$ 2,587,450	$ 2,465,351
Less: Accumulated depreciation	(1,824,534)	(1,415,472)
Total capital leases, net	762,916	1,049,879
Future minimum rental payments under capital leases
2017	176,022
2018	83,603
2019	14,031
2020	5,244
2021	2,185
Total minimum lease payments	281,085
Net minimum lease payments	281,085
Less: Amounts representing interest payments	(12,242)
Present value of net minimum lease payments	268,843
Computer hardware
Analysis of the leased property under capital leases
Total capital leases, gross	2,267,950	2,145,668
Computer software
Analysis of the leased property under capital leases
Total capital leases, gross	$ 319,500	$ 319,683

Amount before accumulated depreciation of leased physical assets used in the normal conduct of business to produce goods and services.

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The total gross amount less the charge for the use of the long-lived depreciable assets subject to a lease meeting the criteria for capitalization.

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Amount of minimum lease payments for capital leases.

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Amount of minimum lease payments for capital leases due in the next fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount of minimum lease payments for capital leases due in the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount of minimum lease payments for capital leases due in the fourth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount of minimum lease payments for capital leases due in the third fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount of minimum lease payments for capital leases due in the second fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount necessary to reduce net minimum lease payments to present value for capital leases.

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Amount of minimum lease payments for capital leases net of executory costs, which include amounts paid by the lessee to the lessor for insurance, maintenance and taxes.

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Present value of minimum lease payments for capital leases net of executory costs, including amounts paid by the lessee to the lessor for insurance, maintenance and taxes.

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The total charge for the use of long-lived depreciable assets subject to a lease meeting the criteria for capitalization.

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