Stock-Based Compensation (Tables)

6 Months Ended

Jun. 30, 2018

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

Schedule of stock-based compensation expense

Stock-based compensation expense is included in the consolidated statements of operations as follows (in thousands):

	Three Months Ended June 30,				Six Months Ended June 30,
	2018		2017		2018		2017
Research and development	$	567	$	342	$	1,003	$	664
Selling, general and administrative	1,890		1,369		3,434		2,715
Total	$	2,457	$	1,711	$	4,437	$	3,379

Schedule of stock-based compensation expense by security types

The following table presents total stock-based compensation expense by security types included in the unaudited condensed consolidated statements of operations 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
Stock options	$	535	$	380	$	1,015	$	714
RSUs and RSAs	436		484		878		943
PSUs	426		348		844		988
PBOs	1,060		499		1,700		734
Total	$	2,457	$	1,711	$	4,437	$	3,379

Valuation assumptions

The weighted-average assumptions used to estimate the fair value of employee stock options and PBOs granted were as follows:

	Three Months Ended June 30,		Six Months Ended June 30,
	2018	2017	2018			2017
	(1)	(1)
Expected term (in years)	—	—	5.6			5.3
Volatility	—	—	60		%	62		%
Risk-free interest rate	—	—	2.70		%	2.00		%
Dividend yield	—	—	—		%	—		%
Weighted-average estimated fair value of stock options granted	—	—	$	5.02		$	2.52

⁽¹⁾ The Company did not grant employee stock options or PBOs in the three months ended June 30, 2018 and 2017.