Equity Transactions and Share-based Compensation (Tables)

6 Months Ended

Jun. 30, 2018

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Schedule of employee and non-employee share-based compensation expense recognized related to stock options, the ESPP and RSUs

Total share-based compensation expense recognized related to stock options, the ESPP and RSUs was as follows (in thousands): 

	Three Months Ended June 30,				Six Months Ended June 30,
	2018		2017		2018		2017
Research and development expense	$	1,536	$	1,852	$	2,856	$	3,615
General and administrative expense	2,500		2,381		4,571		4,645
Total share-based compensation expense	$	4,036	$	4,233	$	7,427	$	8,260