Common stock (Tables)

9 Months Ended

Sep. 30, 2014

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Schedule of Weighted Average Assumptions

The fair value of stock options granted is estimated using the Black-Scholes option pricing model with the following weighted average assumptions:

	THREE MONTHS ENDED SEPTEMBER 30,					NINE MONTHS ENDED SEPTEMBER 30,
	2014			2013		2014			2013
Expected volatility		108	%		n/a		108	%		93	%
Expected dividends		0	%		n/a		0	%		0	%
Expected terms (years)		6.00			n/a		6.00			6.25
Risk free rate		1.70	%		n/a		1.67	%		1.88	%
Weighted average grant-date fair value of stock options	$	6.16			n/a	$	8.33		$	2.92