Stock-Based Compensation (Tables)

9 Months Ended

Sep. 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 September 30,				Nine Months Ended September 30,
	2016		2015		2016		2015
Research and development	$	246	$	181	$	688	$	710
Selling, general and administrative	984		1,042		3,173		3,049
Total	$	1,230	$	1,223	$	3,861	$	3,759

Schedule of stock-based compensation expense by security types

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



	Three Months Ended September 30,				Nine Months Ended September 30,
	2016		2015		2016		2015
Stock options	$	249	$	281	$	820	$	798
RSUs and RSAs	445		566		1,580		2,020
PSUs	536		376		1,461		941
Total	$	1,230	$	1,223	$	3,861	$	3,759

Valuation assumptions

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



	Three Months Ended September 30,						Nine Months Ended September 30,
	2016			2015			2016			2015
Expected term (in years) ⁽¹⁾	5.2			5.2			5.4			6.0
Volatility	63		%	67		%	65		%	66		%
Risk-free interest rate	1.18		%	1.64		%	1.29		%	1.70		%
Dividend yield	—		%	—		%	—		%	—		%
Weighted-average estimated fair value of stock options granted	$	2.25		$	2.31		$	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.")