Stock-based Compensation

9 Months Ended

Sep. 30, 2020

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

9. Stock-based Compensation

During the three and nine months ended September 30, 2020 and 2019, the Company recognized the following stock-based compensation expense (in thousands):

	Three Months Ended September 30,				Nine Months Ended September 30,
	2020		2019		2020		2019
Research and development	$	9,109	$	6,262	$	24,492	$	17,137
General and administrative		8,131		5,081		22,596		15,063
Loss from equity method investment		-		3,430		-		5,467
Total	$	17,240	$	14,773	$	47,088	$	37,667

Stock option activity

The following table summarizes stock option activity for the nine months ended September 30, 2020:

	Shares (in thousands)			Weighted- average exercise price per share
Outstanding at December 31, 2019		7,782,437		$	31.30
Granted		1,468,758		$	56.19
Exercised		(1,011,236	)	$	22.34
Cancelled or forfeited		(307,053	)	$	41.35
Outstanding at September 30, 2020		7,932,906		$	36.66
Exercisable at September 30, 2020		3,741,338		$	28.68
Vested and expected to vest at September 30, 2020		7,932,906		$	36.66

As of September 30, 2020, total unrecognized compensation expense related to stock options was $105.5 million, which the Company expects to recognize over a remaining weighted-average period of 2.6 years.

Restricted stock activity

The following table summarizes restricted stock activity for the nine months ended September 30, 2020:

	Restricted Stock			Weighted- Average Grant Date Fair Value
Unvested balance as of December 31, 2019		699,534		$	56.53
Granted		306,220			49.01
Vested		(74,583	)		50.60
Cancelled or forfeited		(33,661	)		46.23
Unvested balance as of September 30, 2020		897,510		$	54.84

As of September 30, 2020, total unrecognized compensation expense related to unvested restricted common shares was $31.6 million, which the Company expects to recognize over a remaining weighted-average vesting period of 2.0 years.