Segment and Geographical Information - Gross Billings, Based on Billing Address of Clients or Client Affiliates (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Revenues From External Customers And Long Lived Assets [Line Items]
Gross Billings	$ 6,129,627	$ 4,168,260	$ 3,095,687
US
Revenues From External Customers And Long Lived Assets [Line Items]
Gross Billings	5,286,191	3,605,665	2,639,497
International
Revenues From External Customers And Long Lived Assets [Line Items]
Gross Billings	$ 843,436	$ 562,595	$ 456,190