Stock-Based Compensation (Tables)

6 Months Ended

Jun. 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		370,456
Vested		(13,250	)
Forfeited		(43,240	)
Outstanding as of June 30, 2019		396,666

Summary of Stock-Based Compensation Expense for Stock Options, Restricted Stock Units and Employee Stock Purchase Plan Recognized

Stock-based compensation expense for stock options, restricted stock units and the employee stock purchase plan recognized during the three and six months ended June 30, 2019 and 2018 was as follows:

	Three Months Ended June 30,				Six Months Ended June 30,
	2019		2018		2019		2018
	(in thousands)
Research and development	$	13,672	$	12,095	$	34,417	$	20,994
Selling, general and administrative		21,095		16,933		44,466		23,851
	$	34,767	$	29,028	$	78,883	$	44,845

Summary of Stock-Based Compensation Expense by Award Type Recognized

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

	Three Months Ended June 30,				Six Months Ended June 30,
	2019		2018		2019		2018
	(in thousands)
Stock options	$	34,280	$	28,627	$	77,844	$	44,007
Restricted stock units		—		155		58		324
Employee stock purchase plan		487		246		981		514
	$	34,767	$	29,028	$	78,883	$	44,845

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		1,355,931			—
Exercised		(745,558	)		—
Forfeited		(281,850	)		—
Outstanding as of June 30, 2019		7,859,290		$	107.81		7.98	$	600,965
Exercisable as of June 30, 2019		3,321,049		$	70.02		6.89	$	378,713