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Stock-Based Compensation (Tables)
 3 Months Ended
Mar. 31, 2021
Share-based Payment Arrangement [Abstract]  
Stock-based Compensation Expense and Related Income Tax Benefit Stock-based compensation expense by statement of operations caption and the related income tax benefit were as follows:
Three Months Ended March 31,
(In thousands)20212020
Cost of sales$37 $74 
Research and development expenses313 236 
Selling, general and administrative expenses:
Employees
1,868 1,583 
Outside directors
382 410 
Total employee and director stock-based compensation expense$2,600 $2,303 
Income tax benefit$466 $506 
Stock Option Activity
Stock option activity was as follows:    
Number of Options
(in thousands)		Weighted-Average Exercise PriceWeighted-Average Remaining Contractual Term
(in years)		Aggregate Intrinsic Value
(in thousands)
Outstanding at December 31, 2020
774 $43.01 
Granted80 59.43 
Exercised(22)44.39 $253 
Forfeited/canceled/expired— — 
Outstanding at March 31, 2021 (1)
832 $44.56 3.78$10,513 
Vested and expected to vest at March 31, 2021 (1)
832 $44.56 3.78$10,513 
Exercisable at March 31, 2021 (1)
616 $43.68 2.94$8,444 
(1)The aggregate intrinsic value represents the total pre-tax value (the difference between our closing stock price on the last trading day of the first quarter of 2021 and the exercise price, multiplied by the number of in-the-money options) that would have been received by the option holders had they all exercised their options on March 31, 2021. This amount will change based on the fair market value of our stock.
Assumptions Used in Valuation and Weighted Average Fair Value of Stock Option Grants
The assumptions we utilized in the Black-Scholes option pricing model and the resulting weighted average fair value of stock option grants were the following:
 Three Months Ended March 31,
 20212020
Weighted average fair value of grants$23.97 $17.70 
Risk-free interest rate0.41 %1.44 %
Expected volatility48.49 %43.95 %
Expected life in years4.624.59
Non-Vested Restricted Stock Award Activity
Non-vested restricted stock award activity was as follows:
Shares
(in thousands)		Weighted-Average Grant Date Fair Value
Non-vested at December 31, 2020
$374 $34.53 
Granted113 59.67 
Vested(160)34.90 
Forfeited(1)31.83 
Non-vested at March 31, 2021
$326 $43.13