Operating Segments and Geographic Information - Summary of Revenues and Significant Expenses by Segment (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Segment Reporting Information [Line Items]
Revenues	$ 3,566,324	$ 3,900,125	$ 3,646,342
Compensation and benefits	2,040,382	2,277,899	2,146,686
Reimbursable expenses	521,757	486,639	396,164
Other segment items	821,509	895,533	806,003
Impairment of goodwill and indefinite-lived asset	275,170	43,500	1,572,523
Depreciation and amortization	204,553	208,856	216,046
Income from equity method investments	(2,064)
Deconsolidation of European joint venture		(58,891)
Loss on divestiture	0	0	2,863
Total operating expenses	3,861,307	3,853,536	5,140,285
Operating (loss) income from continuing operations	(294,983)	46,589	(1,493,943)
Branded Services [Member]
Segment Reporting Information [Line Items]
Revenues	1,306,336	1,758,417	1,764,076
Compensation and benefits	719,089	1,009,334	994,007
Reimbursable expenses	171,766	179,029	178,474
Other segment items	330,736	417,320	370,628
Impairment of goodwill and indefinite-lived asset	275,170	43,500	831,008
Depreciation and amortization	130,212	140,932	144,354
Income from equity method investments	(2,064)
Deconsolidation of European joint venture		(58,891)
Loss on divestiture			2,863
Total operating expenses	1,624,909	1,731,224	2,521,334
Operating (loss) income from continuing operations	(318,573)	27,193	(757,258)
Experiential Services [Member]
Segment Reporting Information [Line Items]
Revenues	1,295,029	1,159,449	904,230
Compensation and benefits	701,906	638,081	523,517
Reimbursable expenses	349,991	307,610	217,690
Other segment items	201,149	173,879	142,565
Impairment of goodwill and indefinite-lived asset			354,452
Depreciation and amortization	41,728	36,584	37,906
Total operating expenses	1,294,774	1,156,154	1,276,130
Operating (loss) income from continuing operations	255	3,295	(371,900)
Retailer Services [Member]
Segment Reporting Information [Line Items]
Revenues	964,959	982,259	978,036
Compensation and benefits	619,387	630,484	629,162
Other segment items	289,624	304,334	292,810
Impairment of goodwill and indefinite-lived asset			387,063
Depreciation and amortization	32,613	31,340	33,786
Total operating expenses	941,624	966,158	1,342,821
Operating (loss) income from continuing operations	$ 23,335	$ 16,101	$ (364,785)