UNAUDITED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023
Cash flows from operating activities:
Net Income (Loss), Including Portion Attributable to Nonredeemable Noncontrolling Interest	$ 9,197	$ (4,717)
Adjustments to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract]
Stock-based compensation	38,926	34,615
Depreciation and amortization	112,881	107,795
Operating Lease, Right-of-Use Asset, Amortization Expense	58,052	57,583
Impairment and other losses	1,715	10,562
Deferred income taxes	(3,446)	(5,635)
Adjustment To Deferred Acquisition Consideration	7,950	10,881
Other, net	6,371	(4,248)
Changes in working capital:
Accounts receivable	(6,212)	(25,405)
Expenditures billable to clients	(15,705)	(36,217)
Other assets	(9,068)	6,539
Accounts payable	(94,160)	(49,204)
Accrued expenses and other liabilities	(121,647)	(152,216)
Advance billings	23,984	(1,759)
Increase (Decrease) in Operating Lease Liability	(63,956)	(67,095)
Deferred acquisition related payments	(14,112)	(9,021)
Net Cash Provided by (Used in) Operating Activities, Total	(69,230)	(127,542)
Cash flows from investing activities:
Capital expenditures	(16,728)	(12,205)
Acquisitions, net of cash acquired	(23,781)	(6,678)
Capitalized software	(19,320)	(19,026)
Other	(6,656)	(6,939)
Net Cash Provided by (Used in) Investing Activities, Total	(66,485)	(44,848)
Cash flows from financing activities:
Repayment of borrowings under revolving credit facility	(1,176,000)	(1,250,500)
Proceeds from borrowings under revolving credit facility	1,492,000	1,562,500
Shares repurchased and cancelled	(101,249)	(203,958)
Distributions to noncontrolling interests	(23,583)	(24,538)
Payment of deferred consideration	(28,721)	(31,666)
Purchase of noncontrolling interest	(3,316)
Debt issuance costs		(150)
Net Cash Provided by (Used in) Financing Activities, Total	159,131	51,688
Effect of exchange rate changes on cash and cash equivalents	2,654	(1,182)
Net increase (decrease) in cash and cash equivalents	26,070	(121,884)
Cash and cash equivalents at beginning of period	119,737	220,589
Cash and cash equivalents at end of period	145,807	98,705
Supplemental Cash Flow Information:
Cash income taxes paid	15,660	40,088
Cash interest paid	83,046	63,878
Non-cash investing and financing activities:
Acquisitions of business	8,143
Noncash or Part Noncash Acquisition, Noncontrolling Interest Acquired	10,167
Noncash or Part Noncash Acquisition, Noncash Financial or Equity Instrument Consideration, Shares Issued	341
Non-cash payment on deferred acquisition	$ 18,208	$ 20,119