Stock-Based Compensation (Tables)

6 Months Ended

Jun. 30, 2016

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,
	2016		2015		2016		2015
Research and development	$	222	$	238	$	442	$	529
Selling, general and administrative	1,020		1,013		2,189		2,007
Total	$	1,242	$	1,251	$	2,631	$	2,536

Schedule of Share-based Compensation, Restricted Stock and Restricted Stock Units Activity

The following table presents total stock-based compensation expense by security types included in the condensed consolidated statements of operations for the three and six months ended June 30, 2016 and 2015 (in thousands):



	Three Months Ended June 30,				Six Months Ended June 30,
	2016		2015		2016		2015
Stock options	$	267	$	269	$	571	$	517
RSUs and RSAs	561		662		1,135		1,454
PSUs	414		320		925		565
Total	$	1,242	$	1,251	$	2,631	$	2,536

Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions

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



	Three Months Ended June 30,						Six Months Ended June 30,
	2016			2015			2016			2015
Expected term (in years) ⁽¹⁾	5.3			6.0			5.4			6.0
Volatility	64		%	66		%	65		%	66		%
Risk-free interest rate	1.46		%	1.78		%	1.30		%	1.70		%
Dividend yield	—		%	—		%	—		%	—		%
Weighted-average estimated fair value of stock options granted	$	1.94		$	2.58		$	2.30		$	2.09

(1) We had, due to insufficient historical data, used the “simplified method,” as described in SEC Staff Accounting Bulletin No. 107, "Share-Based Payment", to determine the expected term of all stock options granted from the inception of our equity plans through the first half of 2015. Beginning in the third quarter of 2015, we believe we have sufficient historical data to calculate expected terms for stock options granted. (See Note 2, "Basis of Presentation and Summary of Significant Accounting Policies.")