Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Operating activities
Net income	$ 150,611	$ 107,962	$ 85,520
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	31,536	31,177	38,700
Amortization and impairment of other intangible assets	8,162	10,563	10,306
Acquisition-related contingent consideration	479	2,291	2,164
Provision for doubtful accounts	17,872	15,386	8,912
Non-cash share-based compensation	15,577	16,030	16,920
Amortization of debt discount and issuance costs	5,456	1,984	1,985
Gain on sale of business	9,072	0	0
Gain on sale of business	(13,031)	0	0
Other	769	611	(1,204)
Changes in operating assets and liabilities, net of effects from acquisitions:
Accounts receivable, billed and unbilled	(72,034)	(50,831)	3,471
Notes receivable	8,987	14,928	3,145
Prepaid expenses and other assets	(2,258)	629	(2,840)
Accounts payable, accrued expenses and other	8,908	4,421	3,268
Income taxes	11,941	(25,768)	22,012
Accrued compensation	52,510	1,795	40,350
Billings in excess of services provided	(3,885)	16,447	779
Net cash provided by operating activities	230,672	147,625	233,488
Investing activities
Proceeds from sale of business	50,283	0	0
Payments for acquisition of businesses, net of cash received	0	(8,929)	(1,251)
Purchases of property and equipment	(32,270)	(32,004)	(28,935)
Other	731	295	54
Net cash provided by (used in) investing activities	18,744	(40,638)	(30,132)
Financing activities
Borrowings (repayments) under revolving line of credit, net	(100,000)	30,000	(130,000)
Proceeds from issuance of convertible notes	316,250	0	0
Payments of long-term debt	(300,000)	0	0
Payments of debt issue and debt prepayment costs	(16,149)	0	0
Purchase and retirement of common stock	(55,738)	(168,094)	(21,489)
Net issuance of common stock under equity compensation plans	38,475	(504)	21,708
Payments for acquisition-related contingent consideration	(3,029)	(5,161)	(866)
Deposits and other	2,672	2,825	5,337
Net cash used in financing activities	(117,519)	(140,934)	(125,310)
Effect of exchange rate changes on cash and cash equivalents	(9,789)	7,750	(11,648)
Net increase (decrease) in cash and cash equivalents	122,108	(26,197)	66,398
Cash and cash equivalents, beginning of period	189,961	216,158	149,760
Cash and cash equivalents, end of period	312,069	189,961	216,158
Supplemental cash flow disclosures
Cash paid for interest	21,687	23,285	23,154
Cash paid for income taxes, net of refunds	45,568	4,929	20,270
Non-cash investing and financing activities:
Issuance of stock units under incentive compensation plans	1,059	1,547	1,842
Acquisition-related contingent liability	$ 0	$ 3,426	$ 0