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Fair Value Measurements - Reconciliation of Level 3 Assets (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2021
Dec. 31, 2020
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Beginning of measurement period $ 741,191 $ 714,017
Actual return on plan assets:    
End of measurement period 739,789 741,191
U.S.    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Beginning of measurement period 404,275  
Actual return on plan assets:    
End of measurement period 389,689 404,275
U.K Plan    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Beginning of measurement period 303,954  
Actual return on plan assets:    
End of measurement period 312,119 303,954
Significant Unobservable Inputs (Level 3) | U.S.    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Beginning of measurement period 15,938 14,766
Actual return on plan assets:    
Related to assets still held at the reporting date (3,575) 1,172
Purchases, sales and settlements, net 6,099  
End of measurement period 13,414 15,938
Significant Unobservable Inputs (Level 3) | U.K Plan    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Beginning of measurement period 9,572 9,735
Actual return on plan assets:    
Related to assets still held at the reporting date 1,683 (163)
Purchases, sales and settlements, net 0  
End of measurement period $ 11,255 $ 9,572