Stockholders' equity (Tables)

3 Months Ended

Mar. 31, 2016

Equity [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, 2015		865,457		$	9.75		7.56	$	2,393
Options granted		396,960			8.29
Options forfeited		(6,844	)		12.25
Outstanding at March 31, 2016		1,255,573		$	9.27		8.13	$	999
Exercisable as of March 31, 2016		510,584		$	8.87		6.51	$	677

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 MARCH 31,
	2016			2015
Expected volatility		80	%		98	%
Expected dividends		0	%		0	%
Expected terms (years)		6.00			6.00
Risk free rate		1.27	%		1.49	%
Weighted average grant-date fair value of stock options	$	5.67		$	9.21