Net loss per share attributable to common stockholders - Summary of outstanding shares of common stock equivalents excluded from computation of diluted net loss per share (Details 1) - shares	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Weighted average shares outstanding:
Total	2,732,501	1,482,065
Common stock warrants
Weighted average shares outstanding:
Total	687,599	359,868
Options
Weighted average shares outstanding:
Total	2,044,902	1,122,197