STOCK-BASED COMPENSATION

9 Months Ended

Sep. 30, 2019

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

10. STOCK-BASED COMPENSATION

The following table summarizes the Company’s stock awards granted for each of the periods indicated:

	For the Three Months Ended September 30,								For the Nine Months Ended September 30,
	2019				2018				2019				2018
	Grants		Weighted Average Grant Date Fair Value		Grants		Weighted Average Grant Date Fair Value		Grants		Weighted Average Grant Date Fair Value		Grants		Weighted Average Grant Date Fair Value
Stock options		152,248	$	51.64		359,182	$	68.31		1,297,747	$	72.50		2,011,863	$	43.17
Restricted stock units		78,073	$	99.52		5,990	$	138.04		483,703	$	132.45		175,410	$	76.27
Restricted stock awards		—	$	—		10,500	$	142.71		—	$	—		27,590	$	98.57

Stock-based Compensation Expense

For the three months ended September 30, 2019 and 2018, total stock-based compensation expense was $20.6 million and $11.5 million, respectively. For the nine months ended September 30, 2019 and 2018, total stock-based compensation expense was $56.5 million and $37.3 million, respectively. The following table summarizes stock-based compensation expense by function included within the unaudited condensed consolidated statements of operations and comprehensive loss:

	For the Three Months Ended September 30,				For the Nine Months Ended September 30,
	2019		2018		2019		2018
	(in thousands)
Research and development	$	6,972	$	3,260	$	18,982	$	10,349
Selling, general and administrative		13,665		8,224		37,556		26,940
Total stock-based compensation expense	$	20,637	$	11,484	$	56,538	$	37,289

The following table summarizes stock-based compensation expense by grant type included within the unaudited condensed consolidated statements of operations and comprehensive loss:

	For the Three Months Ended September 30,				For the Nine Months Ended September 30,
	2019		2018		2019		2018
	(in thousands)
Stock options	$	13,941	$	9,007	$	39,175	$	27,362
Restricted stock awards/units		5,233		1,987		14,333		8,654
Employee stock purchase plan		1,463		490		3,030		1,273
Total stock-based compensation expense	$	20,637	$	11,484	$	56,538	$	37,289