CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Cash flows from operating activities:
Net Income (Loss), Including Portion Attributable to Nonredeemable Noncontrolling Interest	$ 30,626	$ 25,044	$ 41,642
Adjustments to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract]
Stock-based compensation	54,095	52,161	57,179
Depreciation and amortization	171,249	151,652	142,831
Operating Lease, Right-of-Use Asset, Amortization Expense	67,495	75,117	76,653
Impairment and other losses	(3,116)	1,715	11,395
Gain (loss) on disposition of business	2,245	0	(94,505)
Business Combination, Bargain Purchase, Gain Recognized, Amount	(9,937)
Deferred income taxes	10,439	(10,686)	19,443
Adjustment To Deferred Acquisition Consideration	(7,467)	23,005	13,060
Other, net	7,519	7,622	8,313
Changes in working capital:
Accounts receivable	28,787	8,465	(58,704)
Expenditures billable to clients	12,012	(54,350)	(21,477)
Other current assets	(51,534)	(6,200)	1,153
Accounts payable	73,573	24,438	52,837
Accrued expenses and other liabilities	(42,244)	(28,658)	(24,647)
Advance billings	25,574	(22,651)	(41,137)
Increase (Decrease) in Operating Lease Liability	(76,465)	(83,905)	(87,629)
Deferred acquisition related payments	(1,823)	(19,910)	(15,400)
Net Cash Provided by (Used in) Operating Activities, Total	291,028	142,859	81,007
Cash flows from investing activities:
Capitalized software	(67,489)	(35,094)	(28,175)
Capital expenditures	(43,741)	(18,912)	(14,238)
Acquisitions, net of cash acquired	(6,179)	(103,254)	(23,339)
Proceeds from sale of business, net	10,850	0	229,484
Other	(7,119)	(5,212)	(7,781)
Net Cash Provided by (Used in) Investing Activities, Total	(113,678)	(162,472)	155,951
Cash flows from financing activities:
Repayment of borrowings under revolving credit facility	(2,026,000)	(1,755,000)	(1,986,500)
Proceeds from borrowings under revolving credit facility	1,999,326	1,960,000	1,945,500
Shares repurchased and cancelled	(134,261)	(108,249)	(223,835)
Distributions to noncontrolling interests	(9,662)	(26,723)	(24,964)
Payment of deferred consideration	(33,343)	(29,774)	(49,221)
Proceeds from (Payments to) Noncontrolling Interests	0	(3,316)	0
Payments of Financing Costs	(6,077)	0	(844)
Net Cash Provided by (Used in) Financing Activities, Total	(210,017)	36,938	(339,864)
Effect of exchange rate changes on cash and cash equivalents	5,865	(5,723)	2,054
Net increase (decrease) in cash and cash equivalents	(26,802)	11,602	(100,852)
Cash and cash equivalents at beginning of period	131,339	119,737	220,589
Cash and cash equivalents at end of period	104,537	131,339	119,737
Supplemental Cash Flow Information:
Income Taxes Paid	22,952	23,906	45,538
Cash interest paid	94,420	91,050	87,068
Non-cash investing and financing activities:
Shares issued for business acquisitions	15,300	47,082	8,332
Noncash or Part Noncash Acquisition, Noncontrolling Interest Acquired	0	27,207	22,172
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	237,941
Addition to Tax Receivables Agreement liability related to exchange of Paired Units	229,684
Conversion of Class C to Class A shares	447,562
Non-cash payment on deferred acquisition	$ 21,827	$ 18,208	$ 32,820