Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating activities
Net income	$ 107,962	$ 85,520	$ 66,053
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	31,177	38,700	31,392
Amortization and impairment of other intangible assets	10,563	10,306	11,726
Acquisition-related contingent consideration	2,291	2,164	(1,200)
Provision for doubtful accounts	15,386	8,912	15,564
Non-cash share-based compensation	16,030	16,920	17,951
Non-cash interest expense	1,984	1,985	2,521
Loss on early extinguishment of debt	0	0	19,589
Other	611	(1,204)	(760)
Changes in operating assets and liabilities, net of effects from acquisitions:
Accounts receivable, billed and unbilled	(50,831)	3,471	(35,648)
Notes receivable	14,928	3,145	3,106
Prepaid expenses and other assets	629	(2,840)	(3,557)
Accounts payable, accrued expenses and other	4,421	3,268	(4,718)
Income taxes	(25,768)	22,012	18,491
Accrued compensation	1,795	40,350	4,780
Billings in excess of services provided	16,447	779	(5,370)
Net cash provided by operating activities	147,625	233,488	139,920
Investing activities
Payments for acquisition of businesses, net of cash received	(8,929)	(1,251)	(575)
Purchases of property and equipment	(32,004)	(28,935)	(31,399)
Other	295	54	237
Net cash used in investing activities	(40,638)	(30,132)	(31,737)
Financing activities
Borrowings (repayments) under revolving line of credit, net	30,000	(130,000)	200,000
Payments of long-term debt	0	0	(425,671)
Payments of debt issue costs	0	0	(3,843)
Deposits	2,825	4,006	3,227
Purchase and retirement of common stock	(168,094)	(21,489)	(26,532)
Net issuance of common stock under equity compensation plans	(504)	21,708	16,666
Payments for acquisition-related contingent consideration	(5,161)	(866)	(745)
Other	0	1,331	936
Net cash used in financing activities	(140,934)	(125,310)	(235,962)
Effect of exchange rate changes on cash and cash equivalents	7,750	(11,648)	(6,141)
Net increase (decrease) in cash and cash equivalents	(26,197)	66,398	(133,920)
Cash and cash equivalents, beginning of period	216,158	149,760	283,680
Cash and cash equivalents, end of period	189,961	216,158	149,760
Supplemental cash flow disclosures
Cash paid for interest	23,285	23,154	46,965
Cash paid for income taxes, net of refunds	4,929	20,270	20,654
Non-cash investing and financing activities:
Issuance of stock units under incentive compensation plans	1,547	1,842	2,124
Acquisition related contingent liability	$ 3,426	$ 0	$ 0