STOCK-BASED COMPENSATION

6 Months Ended

Jun. 30, 2018

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

12. STOCK-BASED COMPENSATION

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

	For the Three Months Ended June 30,								For the Six Months Ended June 30,
	2018				2017				2018				2017
	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		528,096	$	45.45		3,579,467	$	13.64		1,652,681	$	37.71		4,456,959	$	14.16
Restricted stock units		18,695	$	95.38		20,000	$	36.26		169,420	$	74.09		181,029	$	33.03
Restricted stock awards		—	$	—		335,000	$	34.65		17,090	$	71.45		341,500	$	34.58

Stock-based Compensation Expense

For the three months ended June 30, 2018 and 2017, total stock-based compensation expense was $15.3 million and $10.5 million, respectively. For the six months ended June 30, 2018 and 2017, total stock-based compensation expense was $25.8 million and $16.2 million, respectively. The increase in stock-based compensation expense for both the three and the six months was partially driven by the achievement of a milestone related to the September 2016 restricted stock awards with performance conditions. 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 June 30,				For the Six Months Ended June 30,
	2018		2017		2018		2017
	(in thousands)
Research and development	$	5,029	$	2,195	$	7,089	$	4,069
Selling, general and administrative		10,250		8,270		18,716		12,108
Total stock-based compensation expense	$	15,279	$	10,465	$	25,805	$	16,177

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 June 30,				For the Six Months Ended June 30,
	2018		2017		2018		2017
	(in thousands)
Stock options	$	9,382	$	6,763	$	18,355	$	11,801
Restricted stock awards/units		5,407		3,250		6,667		3,454
Employee stock purchase plan		490		452		783		922
Total stock-based compensation expense	$	15,279	$	10,465	$	25,805	$	16,177