Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Operating activities
Net income	$ 234,966	$ 210,682	$ 216,726
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	34,269	32,661	30,153
Amortization and impairment of intangible assets	10,823	10,387	8,152
Acquisition-related contingent consideration	(324)	5,593	2,372
Provision for expected credit losses	16,151	19,692	19,602
Share-based compensation	23,051	22,904	17,978
Amortization of debt discount and issuance costs and other	11,701	11,259	11,917
Deferred income taxes	4,958	(9,132)	(3,712)
Changes in operating assets and liabilities, net of effects from acquisitions:
Accounts receivable, billed and unbilled	(61,274)	(26,800)	(141,894)
Notes receivable	12,645	8,029	10,445
Prepaid expenses and other assets	(1,165)	4,640	(22,648)
Accounts payable, accrued expenses and other	(2,102)	13,901	(8,907)
Income taxes	10,523	(22,549)	24,496
Accrued compensation	59,566	38,627	61,339
Billings in excess of services provided	1,695	7,175	(8,133)
Net cash provided by operating activities	355,483	327,069	217,886
Investing activities
Payments for acquisition of businesses, net of cash received	(10,428)	(25,271)	(18,791)
Purchases of property and equipment and other	(68,665)	(34,849)	(41,815)
Net cash used in investing activities	(79,093)	(60,120)	(60,606)
Financing activities
Borrowings under revolving line of credit	402,500	289,500	45,000
Repayments under revolving line of credit	(402,500)	(289,500)	(45,000)
Purchase and retirement of common stock	(46,133)	(353,593)	(105,797)
Share-based compensation tax withholdings and other	(9,246)	(5,823)	3,171
Payments for business acquisition liabilities	(7,496)	(3,948)	(2,282)
Deposits and other	1,201	3,311	1,597
Net cash used in financing activities	(61,674)	(360,053)	(103,311)
Effect of exchange rate changes on cash and cash equivalents	(15,184)	18,684	3,335
Net increase (decrease) in cash and cash equivalents	199,532	(74,420)	57,304
Cash and cash equivalents, beginning of period	294,953	369,373	312,069
Cash and cash equivalents, end of period	494,485	294,953	369,373
Supplemental cash flow disclosures
Cash paid for interest	9,102	7,752	7,606
Cash paid for income taxes, net of refunds	47,500	83,445	50,941
Non-cash investing and financing activities:
Issuance of stock units under incentive compensation plans	2,603	2,314	1,413
Business acquisition liabilities not yet paid	1,093	6,209	9,746
Non-cash additions to property and equipment	$ 6,518	$ 4,966	$ (2,742)