Stock-Based Compensation (Tables)

6 Months Ended

Jun. 30, 2018

Stock-Based Compensation [Abstract]

Stock-Based Compensation Expense

The following table summarizes stock-based compensation expense for the three and six months ended June 30, 2018 and 2017 (in thousands):

	Three Months Ended June 30,				Six Months Ended June 30,
	2018		2017		2018		2017
Research and development expenses	$	2,242	$	1,919	$	4,555	$	3,520
General and administrative expenses		9,884		2,023		13,954		3,602
Total	$	12,126	$	3,942	$	18,509	$	7,122