Stockholders' Equity (Tables)

3 Months Ended

Mar. 31, 2018

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 Income was as follows (in thousands):



	Three months ended March 31,
	Three months ended March 31,
	2018		2017
Cost of sales	$	231	$	130
Research and development	592		412
Sales and marketing	796		470
General and administrative	1,317		909
Total stock-based compensation expense	$	2,936	$	1,921

Estimated Fair Value of Each Stock Option Award

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



	Three months ended March 31,
	2018		2017
Risk-free interest rate	2.49	%	2.33	%
Expected option life (in years)	6.29		6.63
Volatility rate	36	%	36	%
Dividend rate	—	%	—	%