Stock-based compensation (Tables)

9 Months Ended

Sep. 30, 2015

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Summary of Stock Based Compensation Expense

The following table summarizes the stock-based compensation expense recognized in the three and nine months ended September 30, 2015 and 2014 (in thousands):

	Three Months Ended				Nine Months Ended
	September 30,				September 30,
	2015		2014		2015		2014
Cost of goods sold	$	339	$	203	$	1,119	$	988
Research and development		363		339		1,357		1,454
Sales and marketing		275		417		1,175		1,377
General and administrative		459		229		1,767		993
	$	1,436	$	1,188	$	5,418	$	4,812

Estimated Fair Value of Certain Stock-Based Awards Using Black-Scholes-Merton Valuation Model

The Company estimated the fair value of certain stock-based awards using a Black-Scholes-Merton valuation model with the following assumptions:

	Three Months Ended September 30,		Nine Months Ended September 30,
Stock options	2015	2014	2015	2014
Weighted-average expected term (years)	5.6	5.8	5.4	5.5
Weighted-average volatility	63%	66%	64%	68%
Risk-free interest rate	1.63% - 1.85%	1.62% - 1.88%	1.37% – 1.85%	1.62% – 1.88%
Expected dividends	—	—	—	—
Stock appreciation units
Weighted-average expected term (years)	3.5	2.5	3.6	2.5
Weighted-average volatility	60%	54%	62%	56%
Risk-free interest rate	0.28% – 1.38%	0.47% – 0.88%	0.25% – 1.57%	0.13% – 0.90%
Expected dividends	—	—	—	—
ESPP
Weighted-average expected term (years)	—	—	0.7	0.7
Weighted-average volatility	—	—	58%	54%
Risk-free interest rate	—	—	0.03%-0.14%	0.05% – 0.13%
Expected dividends	—	—	—	—

Summary of Stock Option and Restricted Stock Unit Activity

The following table summarizes the Company’s stock option and RSU activity during the nine months ended September 30, 2015:

	Stock Options			Restricted Stock Units
		Weighted			Weighted
		Average			Average
	Number of	Exercise		Number of	Grant Date
	Shares	Price		Units	Fair Value
Balance at December 31, 2014	4,899,713	$	4.07	655,729	$	6.19
Granted	256,780	$	5.27	204,434	$	6.66
Exercised/Converted	(102,711)	$	4.32	(547,828)	$	6.05
Cancelled/Forfeited	(126,677)	$	4.67	(23,602)	$	5.37
Balance at September 30, 2015	4,927,105	$	4.11	288,733	$	6.85