Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Operating activities
Net income	$ 155,093	$ 187,665
Adjustments to reconcile net income to net cash provided by operating    activities:
Depreciation and amortization	23,655	22,384
Amortization and impairment of other intangible assets	7,440	5,838
Acquisition-related contingent consideration	4,652	717
Provision for doubtful accounts	15,608	13,552
Share-based compensation	17,576	14,060
Amortization of debt discount and issuance costs	9,028	8,666
Deferred income taxes	(1,658)	4,084
Other	45	248
Changes in operating assets and liabilities, net of effects from    acquisitions:
Accounts receivable, billed and unbilled	(86,491)	(191,644)
Notes receivable	3,346	2,521
Prepaid expenses and other assets	8,294	(5,817)
Accounts payable, accrued expenses and other	7,713	(7,332)
Income taxes	(14,635)	26,693
Accrued compensation	(18,985)	5,156
Billings in excess of services provided	10,296	(9,925)
Net cash provided by operating activities	140,977	76,866
Investing activities
Payments for acquisition of businesses, net of cash received	(25,271)	(18,791)
Purchases of property and equipment	(25,663)	(27,026)
Other	558	55
Net cash used in investing activities	(50,376)	(45,762)
Financing activities
Borrowings under revolving line of credit	149,500	45,000
Repayments under revolving line of credit	(124,500)	(45,000)
Purchase and retirement of common stock	(175,832)	(77,949)
Net issuance of common stock under equity compensation plans	(5,195)	3,176
Payments for business acquisition liabilities	(3,948)	(2,282)
Deposits and other	4,561	535
Net cash used in financing activities	(155,414)	(76,520)
Effect of exchange rate changes on cash and cash equivalents	98	(8,183)
Net decrease in cash and cash equivalents	(64,715)	(53,599)
Cash and cash equivalents, beginning of period	369,373	312,069
Cash and cash equivalents, end of period	304,658	258,470
Supplemental cash flow disclosures
Cash paid for interest	7,115	7,264
Cash paid for income taxes, net of refunds	61,636	29,885
Non-cash investing and financing activities:
Issuance of stock units under incentive compensation plans	2,314	1,413
Purchase and retirement of common stock not yet paid	8,540	0
Business acquisition liabilities not yet paid	$ 3,460	$ 14,004