Stockholders' equity (Tables)

9 Months Ended

Sep. 30, 2015

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

Schedule of Stock Option Transactions and Number of Stock Options Outstanding

Stock option transactions and the number of stock options outstanding are summarized below:

	NUMBER OF SHARES			WEIGHTED AVERAGE EXERCISE PRICE		WEIGHTED AVERAGE REMAINING CONTRACTUAL LIFE (IN YEARS)		AGGREGATE INTRINSIC VALUE
Outstanding at December 31, 2014		824,604		$	6.79		7.16	$	789
Options granted		287,750			11.46
Options exercised		(191,878	)		5.99
Options forfeited		(49,349	)		9.58
Options expired		(12,170	)		9.26
Outstanding at September 30, 2015		858,957		$	9.72		7.80	$	3,736
Exercisable at September 30, 2015		152,802		$	9.29		6.37	$	2,231

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,
	2015		2014	2015	2014
Expected volatility		NA	108%	98%	108%
Expected dividends		NA	0%	0%	0%
Expected terms (years)		NA	6.00	6.40	6.00
Risk free rate		NA	1.70%	1.48%	1.67%
Weighted average grant-date fair value of stock options		NA	$6.16	$9.02	$8.33