Stock-Based Compensation (Tables)

9 Months Ended

Sep. 30, 2021

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Summary of Time Based and Performance-Based Stock Compensation Expense

The following table summarizes time-based and performance-based stock compensation expense reflected in the consolidated statements of operations:

	Three Months Ended				Nine Months Ended
	September 30				September 30
	2021		2020		2021		2020
	(in thousands)
Research and development	$	5,403	$	4,279	$	17,474	$	23,322
General and administrative		8,254		7,301		24,106		22,362
Total stock compensation expense	$	13,657	$	11,580	$	41,580	$	45,684

Summary of Restricted Stock Units Activity

The following table summarizes RSU activity as of September 30, 2021, under the Second Amended and Restated Long Term Incentive Plan (LTIP Plan) agreement:

	Number of RSUs			Weighted-Average Grant Date Fair Value
Outstanding at January 1, 2021		108,551		$	115.54
Granted		301,366			120.25
Vested		(7,661	)		174.67
Forfeited		(34,710	)		127.57
Outstanding at September 30, 2021		367,546		$	117.03

Summary of Stock Option Activity

The following table summarizes stock option activity as of September 30, 2021, under the LTIP Plan and standalone option agreements:

	Number of Options			Weighted- Average Price
Outstanding at January 1, 2021		4,306,269		$	79.47
Granted		914,179			123.78
Exercised		(229,543	)		39.09
Forfeited		(237,872	)		126.23
Expired		(47,518	)		203.57
Outstanding at September 30, 2021		4,705,515		$	86.43
Exercisable at September 30, 2021		2,637,621		$	53.51