Subsequent events (Details) (Subsequent Event, USD $)	0 Months Ended	1 Months Ended
	May 08, 2015	Apr. 30, 2015
Initial public offering
Subsequent events
Number of units issued under initial public offering	2,850,000
Composition of initial public offering unit, number of shares of common stock	1
Number of common shares that can be acquired upon exercise of each warrant	1
Purchase price of units issued under initial public offering (in dollars per unit)	$ 6.00
Gross proceeds from issuance of IPO	$ 17,100,000
Demand notes converted to equity	2,100,000
Net proceeds from issuance of IPO, after considering demand notes, underwriting discounts and commissions and offering expenses	12,800,000
Initial public offering | Sales and marketing activities
Subsequent events
Net proceeds from issuance of IPO, after considering demand notes, underwriting discounts and commissions and offering expenses	5,000,000
Initial public offering | Research and development
Subsequent events
Net proceeds from issuance of IPO, after considering demand notes, underwriting discounts and commissions and offering expenses	$ 4,000,000
Initial public offering | Common stock
Subsequent events
Common stock shares issued on conversion	7,374,864
Over-Allotment Option | Warrant
Subsequent events
Sale of common stock shares	422,500
2015 Plan | Common stock
Subsequent events
Number of shares authorized under the plan		1,355,000
Additional shares authorized based on outstanding shares (as a percent)		4.00%