Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Operating activities
Net income	$ 216,726	$ 150,611	$ 107,962
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	30,153	31,536	31,177
Amortization and impairment of other intangible assets	8,152	8,162	10,563
Acquisition-related contingent consideration	2,372	479	2,291
Provision for doubtful accounts	19,602	17,872	15,386
Share-based compensation	17,978	15,577	16,030
Amortization of debt discount and issuance costs	11,615	5,456	1,984
Loss on early extinguishment of debt	0	9,072	0
Gain on sale of business	0	(13,031)	0
Deferred income taxes	(3,712)	20,831	(51,579)
Other	302	769	611
Changes in operating assets and liabilities, net of effects from acquisitions:
Accounts receivable, billed and unbilled	(141,894)	(72,034)	(50,831)
Notes receivable	10,445	8,987	14,928
Prepaid expenses and other assets	(22,648)	(2,258)	629
Accounts payable, accrued expenses and other	(8,907)	8,908	4,421
Income taxes	24,496	(8,890)	25,811
Accrued compensation	61,339	52,510	1,795
Billings in excess of services provided	(8,133)	(3,885)	16,447
Net cash provided by operating activities	217,886	230,672	147,625
Investing activities
Proceeds from sale of business	0	50,283	0
Payments for acquisition of businesses, net of cash received	(18,791)	0	(8,929)
Purchases of property and equipment	(42,072)	(32,270)	(32,004)
Other	257	731	295
Net cash provided by (used in) investing activities	(60,606)	18,744	(40,638)
Financing activities
Borrowings under revolving line of credit	45,000	233,500	422,000
Repayments under revolving line of credit	(45,000)	(333,500)	(392,000)
Proceeds from issuance of convertible notes	0	316,250	0
Payments of long-term debt	0	(300,000)	0
Payments of debt issue and debt prepayment costs	0	(16,149)	0
Purchase and retirement of common stock	(105,797)	(55,738)	(168,094)
Net issuance of common stock under equity compensation plans	3,171	38,475	(504)
Payments for business acquisition liabilities	(2,282)	(3,029)	(5,161)
Deposits and other	1,597	2,672	2,825
Net cash used in financing activities	(103,311)	(117,519)	(140,934)
Effect of exchange rate changes on cash and cash equivalents	3,335	(9,789)	7,750
Net increase (decrease) in cash and cash equivalents	57,304	122,108	(26,197)
Cash and cash equivalents, beginning of period	312,069	189,961	216,158
Cash and cash equivalents, end of period	369,373	312,069	189,961
Supplemental cash flow disclosures
Cash paid for interest	7,606	21,687	23,285
Cash paid for income taxes, net of refunds	50,941	45,568	4,929
Non-cash investing and financing activities:
Issuance of stock units under incentive compensation plans	1,413	1,059	1,547
Business acquisition liabilities not yet paid	$ 9,746	$ 0	$ 3,426