Share-based compensation (Details Textual) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross	40,500	665,000
Share-based Compensation Arrangements by Share-based Payment Award, Options, Grants in Period, Weighted Average Exercise Price	$ 4.10	$ 4.59
Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures in Period	106,312	3,619
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized	$ 1,327,199
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition	1 year 8 months 19 days
Share-based Compensation	$ 941,031	$ 326,171
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period		294,667
Share-based Compensation Arrangement by Share-based Payment Award, Options, Other Increases (Decreases) in Period	25,382	7,064
Vesting Immediately [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures in Period	12,188
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period	25,382	10,036
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested, Number of Shares	37,570	17,100
Share-based Compensation Arrangement by Share-based Payment Award, Options, Other Increases (Decreases) in Period		7,064
Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Intrinsic Value	$ 38,000	$ 133,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding, Aggregate Intrinsic Value	$ 62,000	$ 298,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross	40,500	665,000
Share-based Compensation Arrangements by Share-based Payment Award, Options, Grants in Period, Weighted Average Exercise Price	$ 4.10	$ 3.10
Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures in Period	106,312	3,619
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period		294,667
Omnibus Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant	2,250,000
Common Stock, Capital Shares Reserved for Future Issuance		2,250,000
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights	The maximum term of options granted under the 2017 Plan is ten years, except that the maximum permitted term of incentive stock options granted to 10% stockholders is five years.