Convertible preferred stock (Details) - shares	Mar. 31, 2017	Dec. 31, 2016	Apr. 11, 2016
Convertible preferred stock
Shares designated (and issued)	1,535,398	1,535,398
Series A Preferred stock
Convertible preferred stock
Number of Series A Preferred Stock converted			708,352
Number of common stock that Series A Preferred Stock converted into			2,162,907
Conversion ratio of common stock per share of Series A Preferred Stock	3.05		3.05
Shares designated (and issued)	1,535,398
Shares undesignated (and unissued)	1,756,250
Number of common shares into which each issued share to be converted	3.05		3.05
Total number of common shares into which issued shares to be converted	4,688,237