Stock-based compensation - Summary of stock-based compensation expense (Details) (USD $)	1 Months Ended	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2015
Employee Service Share-Based Compensation Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 11,935	$ 1,745,760
Research and development
Employee Service Share-Based Compensation Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense	6,558	957,210
General and administrative
Employee Service Share-Based Compensation Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 5,377	$ 788,550