Stock-Based Compensation (Tables)

3 Months Ended

Mar. 31, 2019

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

Schedule of stock-based compensation expense

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

	Three Months Ended March 31,
	2019		2018
Research and development	$	388	$	435
Selling, general and administrative	1,675		1,545
Total	$	2,063	$	1,980

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 months ended March 31, 2019 and 2018 (in thousands):

	Three Months Ended March 31,
	2019		2018
Stock options	$	554	$	472
RSUs and RSAs	461		452
PSUs	391		409
PBOs	657		647
Total	$	2,063	$	1,980

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 March 31,
	2019			2018
Expected term (in years)	5.6			5.6
Volatility	56		%	60		%
Risk-free interest rate	2.49		%	2.70		%
Dividend yield	—		%	—		%
Weighted-average estimated fair value of stock options granted	$	11.44		$	5.02