Stock-Based Compensation (Tables)

9 Months Ended

Sep. 30, 2019

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Summary of Activity Relating to Restricted Stock Units

The table below summarizes activity relating to restricted stock units:

	Shares
Outstanding as of December 31, 2018		82,700
Granted		386,714
Vested		(82,128	)
Forfeited		(52,914	)
Outstanding as of September 30, 2019		334,372

Summary of Stock-Based Compensation Expense Recognized

Stock-based compensation expense recognized during the three and nine months ended September 30, 2019 and 2018 was as follows:

	Three Months Ended September 30,				Nine Months Ended September 30,
	2019		2018		2019		2018
	(in thousands)
Research and development	$	17,111	$	13,997	$	51,528	$	34,991
Selling, general and administrative		26,558		11,481		71,024		35,332
	$	43,669	$	25,478	$	122,552	$	70,323

Summary of Stock-Based Compensation Expense by Award Type Recognized

Stock-based compensation expense recognized during the three and nine months ended September 30, 2019 and 2018 by award type was as follows:

	Three Months Ended September 30,				Nine Months Ended September 30,
	2019		2018		2019		2018
	(in thousands)
Stock options	$	32,119	$	25,015	$	109,963	$	69,023
Restricted stock units		10,934		164		10,992		487
Employee stock purchase plan		616		299		1,597		813
	$	43,669	$	25,478	$	122,552	$	70,323

Summary of Activity Relating to Stock Options

The table below summarizes activity related to stock options:

	Shares			Weighted Average Exercise Price		Weighted Average Remaining Life (in years)		Aggregate Intrinsic Value (in thousands)
Outstanding as of December 31, 2018		7,530,767		$	93.22		8.03	$	227,447
Granted		1,428,948			157.95
Exercised		(971,203	)		43.20
Forfeited		(412,515	)		134.99
Outstanding as of September 30, 2019		7,575,997		$	109.56		7.78	$	327,724
Exercisable as of September 30, 2019		3,473,244		$	75.59		6.79	$	251,232