Stockholders' equity (Tables)

9 Months Ended

Sep. 30, 2019

Federal Home Loan Banks [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 (IN THOUSANDS)
Outstanding at December 31, 2018		2,897,294		$	9.04		7.96	$	—
Options granted		298,000			3.54		0		0
Options exercised		(13,104	)		3.07		0		0
Options forfeited		(278,197	)		11.84		0		0
Outstanding at September 30, 2019		2,903,993		$	8.23		3.95	$	3
Exercisable as of September 30, 2019		2,288,581		$	9.41		3.60	$	0

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,
	2019			2018			2019			2018
Expected volatility		90	%		83	%		90	%		80	%
Expected dividends		0	%		0	%		0	%		0	%
Expected terms (years)		6.00			6.00			6.00			6.00
Risk free rate		1.44	%		2.86	%		1.44	%		2.80	%
Weighted average grant-date fair value of stock options	$	2.63		$	2.20		$	2.63		$	6.25