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Stock-Based Compensation (Tables)
 12 Months Ended
Dec. 31, 2020
Share-based Payment Arrangement [Abstract]  
Summary of Stock Option Activity
The following table summarizes the Company’s stock option activity:
Shares
(in thousands)		Weighted-
Average
Exercise
Price		Weighted-
Average
Remaining
Contractual
Term
(in years)		Aggregate
Intrinsic Value
(in thousands)
Outstanding as of December 31, 201912,899 $37.95 
Granted1,245 54.68 
Exercised(4,565)27.54 
Forfeited or expired(609)50.28 
Outstanding as of December 31, 20208,970 $44.73 7.11$318,873 
Exercisable as of December 31, 20203,135 $33.79 5.60$145,735 
Options vested or expected to vest as of 
 December 31, 2020 (1)		8,235 $44.08 7.01$298,118 
(1) In addition to the vested options, the Company expects a portion of the unvested options to vest at some point in the future. Options expected to vest are calculated by applying an estimated forfeiture rate to the unvested options.
Weighted-Average Assumptions Used in Estimating Fair Values of Stock Options Granted
The fair values of stock options granted in each period presented were estimated using the following weighted-average assumptions:
 Year Ended December 31,
 202020192018
Risk-free rate1.4 %2.7 %2.9 %
Expected dividend yield0.41 %0.39 %0.35 %
Expected volatility37 %37 %39 %
Expected term (in years)6.05.35.4
Nonvested Restricted Stock Shares Activity [Table Text Block]
The following tables summarizes the Company's RSU activity:
Shares
(in thousands)		Weighted-Average
Grant Date Fair Value
Nonvested as of December 31, 2019150 $48.63 
Granted446 52.09 
Vested— — 
Forfeited or expired(42)50.61 
Nonvested as of December 31, 2020554 $51.27 
Stock-Based Compensation Expense
The following table presents the stock-based compensation expense by caption for each period presented on the Consolidated Statements of Operations (in thousands):
 Year Ended December 31,
 202020192018
Cost of revenue$1,365 $1,504 $2,447 
Research, development, and engineering13,387 15,748 14,578 
Selling, general, and administrative27,909 28,337 24,065 
$42,661 $45,589 $41,090