Stockholders' Equity (Tables)

6 Months Ended

Jun. 30, 2015

Compensation Expense Related to Stock-Based Compensation Plans

The compensation expense related to the Company’s stock-based compensation plans included in the accompanying Consolidated Statements of Operations was as follows (in thousands):



	Three months ended June 30,				Six months ended June 30,
	Three months ended June 30,				Six months ended June 30,
	2015		2014		2015		2014
Cost of sales	$	104	$	95	$	341	$	328
Research and development	277		149		294		565
Sales and marketing	375		190		877		480
General and administrative	1,170		808		2,482		2,106
Total stock-based compensation expense	$	1,926	$	1,242	$	3,994	$	3,479

Estimated Fair Value of Each Stock Option Award

The estimated fair value of each stock option award was determined on the date of grant using the Black-Scholes option valuation model with the following weighted-average assumptions for the option grants.



	Six months ended June 30,
	Six months ended June 30,
	2015		2014
Risk-free interest rate	1.47	%	1.58	%
Expected option life (in years)	6.23		5.77
Volatility rate	40	%	42	%
Dividend rate	—	%	—	%