Stock-based compensation (Tables)

9 Months Ended

Sep. 30, 2015

Stock-based compensation [Abstract]

Schedule of Fair Value of Each Option Award Granted

The fair value of each option award granted during the period is estimated on the date of grant using the Black-Scholes option valuation model and assumptions as noted in the following table:

	Nine Months Ended September 30,
	2015	2014
Risk-free interest rate	1.75%	2.14 – 2.45%
Volatility	85.68%	75.51 – 73.87%
Expected dividend yield	0%	0%
Expected life	6.5 years	6.5 years
Estimated forfeiture rate	0%	0%