Stock-Based Compensation

3 Months Ended

Mar. 31, 2020

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

Stock-Based Compensation

Note 10—Stock-Based Compensation

Stock-based compensation expense is as follows:

	Three Months Ended
	March 31,
	2020		2019
	(In thousands)
Research and development	$	1,447	$	1,494
Selling, general and administrative		2,029		1,880
Total	$	3,476	$	3,374

The fair value of each option grant 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
	March 31,
	2020
Estimated weighted-average fair value	$	7.89
Weighted-average assumptions:
Expected volatility		76	%
Expected term, in years		6.0
Risk-free interest rate		1.18	%
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, 2019	11,207,931	$	11.72
Granted	1,744,585		11.95
Exercised	(306,857)		8.84
Forfeited	(54,318)		15.04
Balance at March 31, 2020	12,591,341	$	11.81	6.4	$	26,173
Vested and expected to vest at March 31, 2020	12,116,956	$	11.75	6.3	$	25,838
Exercisable at March 31, 2020	8,261,407	$	11.03	5.0	$	23,067

At March 31, 2020, there were 4.3 million unvested options outstanding that will vest over a weighted-average period of 2.9 years and 3.7 million shares were available to grant. The total estimated compensation expense yet to be recognized on outstanding options is $32.9 million. In March 2020, annual stock option grants totaling approximately 1.6 million shares with an exercise price of $11.91 per share were granted to all eligible employees. The options vest monthly on a straight-line basis over four years.