Accounts receivable, unbilled revenue (contract assets) and unearned revenue or payments on account (contract liabilities) - Schedule of Accounts Receivables and Unbilled Revenue (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Contract Assets [Abstract]
Billed services (accounts receivable)	$ 1,897,771	$ 1,821,855
Allowance for credit losses	(35,303)	(31,533)
Accounts receivable (net)	1,862,468	1,790,322
Unbilled services (unbilled revenue)	993,141	951,936
Accounts receivable and unbilled revenue, net	$ 2,855,609	$ 2,742,258

Accounts receivable, unbilled revenue (contract assets) and unearned revenue or payments on account (contract liabilities) - Schedule of Accounts Receivables and Unbilled Revenue (Details) - USD ($)
$ in Thousands

Mar. 31, 2024

Dec. 31, 2023

Billed services (accounts receivable)

$ 1,897,771

$ 1,821,855

Allowance for credit losses

(35,303)

(31,533)

Accounts receivable (net)

1,862,468

1,790,322

Unbilled services (unbilled revenue)

993,141

951,936

Accounts receivable and unbilled revenue, net

$ 2,855,609

$ 2,742,258