Stock-Based Compensation (Tables)

3 Months Ended

Mar. 31, 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 (in thousands):

	Three Months Ended
	March 31
	2021		2020
Research and development	$	6,808	$	11,516
General and administrative		7,871		7,791
Total stock compensation expense	$	14,679	$	19,307

Summary of Restricted Stock Units Activity

The following table summarizes RSU activity as of March 31, 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		260,408			121.46
Vested		(3,302	)		212.12
Forfeited		(12,199	)		128.19
Outstanding at March 31, 2021		353,458		$	118.56

Summary of Stock Option Activity

The following table summarizes stock option activity as of March 31, 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		697,538			123.39
Exercised		(112,423	)		41.59
Forfeited		(94,271	)		138.30
Expired		(30,727	)		205.84
Outstanding at March 31, 2021		4,766,386		$	84.81
Exercisable at March 31, 2021		2,282,312		$	46.62