Stock-Based Compensation (Tables)

9 Months Ended

Sep. 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 September 30,				Nine Months Ended September 30,
	2018		2017		2018		2017
Research and development	$	552	$	386	$	1,555	$	1,050
Selling, general and administrative	1,218		1,447		4,652		4,162
Total	$	1,770	$	1,833	$	6,207	$	5,212

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 nine months ended September 30, 2018 and 2017 (in thousands):

	Three Months Ended September 30,				Nine Months Ended September 30,
	2018		2017		2018		2017
Stock options	$	472	$	393	$	1,482	$	1,107
RSUs and RSAs	416		456		1,293		1,399
PSUs	407		385		1,251		1,373
PBOs	475		599		2,181		1,333
Total	$	1,770	$	1,833	$	6,207	$	5,212

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 September 30,				Nine Months Ended September 30,
	2018			2017	2018			2017
				(1)
Expected term (in years)	5.7			—	5.6			5.3
Volatility	57		%	—	60		%	62		%
Risk-free interest rate	2.78		%	—	2.70		%	2.02		%
Dividend yield	—		%	—	—		%	—		%
Weighted-average estimated fair value of stock options granted	$	8.39		—	$	5.10		$	2.52

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