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Stock-based Compensation
3 Months Ended
Mar. 31, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]  
Stock-based Compensation
Stock-Based Compensation. Stock-based compensation expense before income tax expense for the three-month periods ended March 31, 2015 and 2014, consisted of the following (in thousands):

 
2015
 
2014
Cost of goods sold
$
93

 
$
43

Research and development
27

 
16

Selling, general, and administrative
400

 
280

Stock-based compensation expense before taxes
$
520

 
$
339



As of March 31, 2015, the total remaining unrecognized compensation cost related to non-vested stock options, net of expected forfeitures, was approximately $6.7 million and is expected to be recognized over a weighted average period of 3.7 years.

During the three months ended March 31, 2015, we granted awards representing 446,800 shares of our common stock. We did not grant any stock-based awards during the three months ended March 31, 2014. We use the Black-Scholes methodology to value the stock-based compensation expense for options. In applying the Black-Scholes methodology to the options granted during the three months ended March 31, 2015, the fair value of our stock-based awards granted was estimated using the following assumptions for the periods indicated below:

 
Three Months Ended
 
March 31, 2015
Risk-free interest rate
1.53%
Expected option life
5.0
Expected dividend yield
—%
Expected price volatility
35.11%


For purposes of the foregoing analysis, the average risk-free interest rate is determined using the U.S. Treasury rate in effect as of the date of grant, based on the expected term of the stock option. The expected term of the stock options is determined using the historical exercise behavior of employees. The expected price volatility is determined using a weighted average of daily historical volatility of our stock price over the corresponding expected option life and implied volatility based on recent trends of the daily historical volatility. Compensation expense is recognized on a straight-line basis over the service period, which corresponds to the related vesting period.