Stock-Based Compensation

9 Months Ended

Sep. 30, 2019

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

Stock-Based Compensation

Note 10—Stock-Based Compensation

Stock-based compensation expense includes the amortization of stock options granted to employees and non-employees and has been reported in our Condensed Consolidated Statements of Operations and Comprehensive Loss as follows:

	Three Months Ended				Nine Months Ended
	September 30,				September 30,
	2019		2018		2019		2018
	(In thousands)				(In thousands)
Research and development	$	1,558	$	1,334	$	4,698	$	3,720
Selling, general and administrative		1,938		1,595		5,770		5,176
Total	$	3,496	$	2,929	$	10,468	$	8,896

The fair value of each option grant to employees, directors and non-employees is estimated on the date of grant using the Black-Scholes option-pricing model. The following assumptions were applied to all stock option grants:

	Three Months Ended						Nine Months Ended
	September 30,						September 30,
	2019			2018			2019			2018
Estimated weighted-average fair value	$	11.81		$	16.30		$	9.91		$	10.22
Weighted-average assumptions:
Expected volatility		79	%		78	%		81	%		77	%
Expected term, in years		6.1			6.1			6.0			6.0
Risk-free interest rate		2.10	%		2.77	%		2.44	%		2.66	%
Expected dividend yield		—	%		—	%		—	%		—	%

Stock option activity for all stock plans and related information is as follows:

		Weighted-
		Average			Aggregate
		Exercise		Remaining	Intrinsic
	Options	Price per		Contractual Life	Value
	Outstanding	Share		(In years)	(In thousands)
Balance at December 31, 2018	10,313,138	$	11.22
Granted	1,956,205		14.17
Exercised	(513,790)		9.80
Forfeited	(260,831)		16.07
Balance at September 30, 2019	11,494,722	$	11.67	6.25	$	56,610
Vested and expected to vest at September 30, 2019	11,126,906	$	11.59	6.17	$	55,668
Exercisable at September 30, 2019	8,117,842	$	10.68	5.20	$	47,725

At September 30, 2019, there were 3,376,880 unvested options outstanding that will vest over a weighted-average period of 2.7 years and 5,396,836 shares were available to grant. The total estimated compensation expense yet to be recognized on outstanding options is $27.4 million.