STOCK-BASED COMPENSATION (Tables)

6 Months Ended

Jun. 30, 2019

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Summary of Stock Awards Granted

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,
	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		155,265	$	67.80		528,096	$	45.45		1,145,499	$	75.27		1,652,681	$	37.71
Restricted stock units		81,000	$	121.34		18,695	$	95.38		405,630	$	138.79		169,420	$	74.09
Restricted stock awards		—	$	—		—	$	—		—	$	—		17,090	$	71.45

Summary of Stock-Based Compensation Expense by Function Included within Condensed Consolidated Statements of Operations and Comprehensive Loss

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,
	2019		2018		2019		2018
	(in thousands)
Research and development	$	6,923	$	5,029	$	12,010	$	7,089
Selling, general and administrative		12,839		10,250		23,891		18,716
Total stock-based compensation expense	$	19,762	$	15,279	$	35,901	$	25,805

Summary of Stock-Based Compensation Expense by Grant Type Included within Condensed Consolidated Statements of Operations and Comprehensive Loss

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,
	2019		2018		2019		2018
	(in thousands)
Stock options	$	13,777	$	9,382	$	25,234	$	18,355
Restricted stock awards/units		5,184		5,407		9,100		6,667
Employee stock purchase plan		801		490		1,567		783
Total stock-based compensation expense	$	19,762	$	15,279	$	35,901	$	25,805