UNAUDITED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024
Cash flows from operating activities:
Net Income (Loss), Including Portion Attributable to Nonredeemable Noncontrolling Interest	$ 13,804	$ 9,197
Adjustments to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract]
Stock-based compensation	44,143	38,926
Depreciation and amortization	127,635	112,881
Operating Lease, Right-of-Use Asset, Amortization Expense	51,208	58,052
Gain (Loss) on Termination of Lease	(3,063)	1,715
Deferred income taxes	3,216	(3,446)
Adjustment To Deferred Acquisition Consideration	(9,911)	7,950
Other, net	1,319	6,371
Changes in working capital:
Accounts receivable	(3,477)	(6,212)
Expenditures billable to clients	26,266	(15,705)
Other assets	(53,377)	(9,068)
Accounts payable	(57,306)	(94,160)
Accrued expenses and other liabilities	(117,118)	(121,647)
Advance billings	67,964	23,984
Increase (Decrease) in Operating Lease Liability	(59,414)	(63,956)
Deferred acquisition related payments	(1,176)	(14,112)
Net Cash Provided by (Used in) Operating Activities, Total	30,713	(69,230)
Cash flows from investing activities:
Capitalized software	(45,315)	(19,320)
Capital expenditures	(26,338)	(16,728)
Acquisitions, net of cash acquired	(6,179)	(23,781)
Other	(2,927)	(6,656)
Net Cash Provided by (Used in) Investing Activities, Total	(80,759)	(66,485)
Cash flows from financing activities:
Repayment of borrowings under revolving credit facility	(1,412,000)	(1,176,000)
Proceeds from borrowings under revolving credit facility	1,586,326	1,492,000
Shares repurchased and cancelled	(105,183)	(101,249)
Distributions to noncontrolling interests	(5,018)	(23,583)
Payment of deferred consideration	(16,103)	(28,721)
Proceeds from (Payments to) Noncontrolling Interests	0	(3,316)
Payments of Financing Costs	(3,795)	0
Net Cash Provided by (Used in) Financing Activities, Total	44,227	159,131
Effect of exchange rate changes on cash and cash equivalents	6,718	2,654
Net increase in cash and cash equivalents	899	26,070
Cash and cash equivalents at beginning of period	131,339	119,737
Cash and cash equivalents at end of period	132,238	145,807
Supplemental Cash Flow Information:
Cash income taxes paid	18,291	15,660
Cash interest paid	86,302	83,046
Non-cash investing and financing activities:
Shares issued for business acquisitions	15,300	8,143
Noncash or Part Noncash Acquisition, Noncontrolling Interest Acquired	0	10,167
Noncash or Part Noncash Acquisition, Noncash Financial or Equity Instrument Consideration, Shares Issued	0	341
Addition to deferred tax asset related to exchange of Paired Units	203,418	0
Addition to Tax Receivables Agreement liability related to exchange of Paired Units	200,274	0
Conversion of Class C to Class A shares	447,562	0
Non-cash payment on deferred acquisition	$ 0	$ 18,208