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Stock-Based Compensation (Tables)
 9 Months Ended
Sep. 30, 2021
Share-based Payment Arrangement [Abstract]  
Summary of Stock Based Compensation Expense
Stock-based compensation expense is summarized as follows:
Three Months Ended September 30,Nine Months Ended September 30,
2021202020212020
(in thousands)
Stock-based compensation expense$5,989 $6,299 $21,833 $16,412 
Summary of Restricted Stock Units Activity
RSU activity, inclusive of PSUs, for the nine months ended September 30, 2021 is summarized as follows: 
Number
of Shares		Weighted Average
Grant Date
Fair Value
Outstanding at December 31, 2020533,185 $106.19 
Granted107,216 $268.56 
Forfeited(22,752)$127.96 
Settled(184,589)$123.17 
Outstanding at September 30, 2021433,060 $138.00