Stockholders' Equity (Tables)

9 Months Ended

Sep. 30, 2019

Equity [Abstract]

Share-based Payment Arrangement, Option, Activity

A summary of the status of stock option activity for the nine months ended September 30, 2019 is as follows (in thousands, except price data):

	Shares		Weighted-average exercise price per share
Outstanding at December 31, 2018	1,877		$	21.53
Granted	169		59.18
Exercised	(628	)	17.28
Forfeited	(3	)	42.29
Outstanding at September 30, 2019	1,415		$	27.89

Schedule of Nonvested Share Activity

A summary of the status of restricted stock unit activity for the nine months ended September 30, 2019 is as follows (in thousands, except price data):

	Shares		Weighted-average grant date fair value
Non-vested at December 31, 2018	676		$	30.75
Granted	255		59.45
Vested	(120	)	25.28
Forfeited	(4	)	46.83
Non-vested at September 30, 2019	807		$	40.52

Compensation Expense Related to Stock-Based Compensation Plans

The 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 September 30,				Nine Months Ended September 30,
	2019		2018		2019		2018
Cost of sales	$	265	$	255	$	807	$	751
Research and development	573		539		1,682		1,732
Sales and marketing	827		686		2,850		2,199
General and administrative	1,459		1,295		4,745		4,508
Total stock-based compensation expense	$	3,124	$	2,775	$	10,084	$	9,190

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.

	Nine Months Ended September 30,
	2019			2018
Risk-free interest rate	2.51		%	2.49		%
Expected option life (in years)	5.7			6.3
Volatility rate	39		%	36		%
Dividend rate	0		%	0		%
Weighted-average grant date fair value	$	23.67		$	18.76