Stock Options (Tables)

12 Months Ended

Dec. 31, 2018

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

Summary of the company's stock option activity and related information

A summary of stock option activity and related information is as follows:

	Options	Weighted Average Exercise Price			Weighted average remaining contractual term (years)	Aggregate intrinsic value (in thousands)
Outstanding at December 31, 2015	1,541,163		$	1.77	6.6
Granted	120,277		$	1.65
Exercised	(109,079)		$	1.74
Forfeited	(54,850)		$	1.87
Outstanding at December 31, 2016	1,497,511		$	1.76	5.8
Granted	721,763		$	0.94
Exercised	(127,122)		$	1.85
Forfeited	(20,536)		$	1.88
Outstanding at December 31, 2017	2,071,616		$	1.47	5.9
Granted	1,014,556		$	31.91
Exercised	(301,058)		$	1.86		$	7,353
Forfeited	(39,958)		$	3.64
Outstanding at December 31, 2018	2,745,156		$	12.64	7.4	$	81,453
Exercisable at December 31, 2018	1,297,075		$	1.54	5.3	$	52,801

Schedule of stock compensation recognized, before taxes

Total stock compensation recognized, before taxes, was as follows:

	Year Ended December 31,
	2018		2017		2016
Research and development	$	51	$	43	$	50
Selling, general and administrative	1,168		200		198
Total stock-based compensation	$	1,219	$	243	$	248

Summary of weighted average assumptions for fair value of options granted

The fair value of options granted to employees and directors during the years ended December 31, 2018, 2017, 2016 was estimated as of the grant date using the Black-Scholes option pricing model using the following assumptions:

	Year Ended December 31,
	2018	2017	2016
Expected life (years)	5.50 - 6.25	5.75 - 6.25	6.25
Expected volatility	37.5 - 49.8%	37.5 - 41.5%	40.6%
Risk-free interest rate	2.38 - 3.07%	1.88 - 2.32%	1.27 - 2.25%
Dividend yield	—%	—%	—%
Weighted average fair value	$16.20	$0.40	$0.47