XML 89 R67.htm IDEA: XBRL DOCUMENT v3.25.0.1
Accounts receivable, unbilled revenue (contract assets) and unearned revenue or payments on account (contract liabilities) - Narrative (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]    
Amounts due to third parties for reimbursable expenses $ 369,200 $ 333,000
Change in unbilled services (unbilled revenue) 334,338  
Change in unearned revenue (payments on account) 39,749  
Decrease in net balance 374,087  
Bad debt expense 28,400 24,600
Revenue, remaining performance obligation, amount $ 15,900,000 $ 14,800,000
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2024-01-01    
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]    
Revenue, remaining performance obligation (in percent)   52.00%
Revenue, remaining performance obligation, expected timing of satisfaction, period   12 months
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2025-01-01    
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]    
Revenue, remaining performance obligation (in percent) 47.00%  
Revenue, remaining performance obligation, expected timing of satisfaction, period 12 months