CONSOLIDATED STATEMENTS OF CASH FLOWS $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Cash Flows from Operating Activities:
Net income	$ 157,706	$ 157,675	$ 97,201
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	94,975	58,604	62,249
Provision for accounts receivable allowances	3,292	12,050	10,788
Provision (benefit) for deferred income taxes	11,215	(5,140)	12,834
Share-based compensation	31,488	24,044	27,024
Workers' Compensation provision	3,577	2,908	2,693
Other	(11,651)	(6,610)	(5,642)
Changes in operating assets and liabilities, net of effects of acquisitions:
Accounts receivable	(90,668)	(50,461)	(43,289)
Prepaid expenses and income taxes	(14,776)	11,861	(6,433)
Income taxes payable	2,135	613	3,346
Accounts payable	23,320	315	(2,236)
Accrued payroll and contract professional pay	25,427	1,040	23,556
Workers' compensation loss reserve	(3,282)	(2,616)	(2,691)
Payments of earn-outs	0	0	(4,780)
Other	1,839	2,665	561
Net cash provided by operating activities	287,451	196,446	199,331
Cash Flows from Investing Activities:
Cash paid for property and equipment	(28,701)	(24,265)	(27,138)
Cash paid for acquisitions, net of cash acquired	(760,216)	(25,940)	0
Cash received from sale of discontinued operations, net	0	0	6,000
Other	184	88	(846)
Net cash used in investing activities	(788,733)	(50,117)	(21,984)
Cash Flows from Financing Activities:
Principal payments of long-term debt	(286,000)	(105,000)	(129,000)
Proceeds from long-term debt	822,000	37,000	11,000
Proceeds from option exercises and employee stock purchase plan	9,372	7,755	9,758
Payment of employment taxes related to release of restricted stock awards	(5,649)	(14,886)	(7,024)
Repurchase of common stock	0	(60,065)	(41,096)
Debt issuance or amendment costs	(22,450)	(3,273)	(889)
Payments of earn-outs	0	0	16,814
Other	(9,474)	0	0
Net cash provided by (used in) financing activities	507,799	(138,469)	(174,065)
Effect of exchange rate changes on cash and cash equivalents	(1,358)	1,763	(107)
Cash and Cash Equivalents, Period Increase (Decrease)	5,159	9,623	3,175
Cash and Cash Equivalents	41,826	36,667	27,044
Supplemental Disclosure of Cash Flow Information
Income taxes	21,399	55,326	38,190
Interest	50,966	24,074	26,829
Non-Cash Investing and Financing Activities:
Unpaid portion of additions to property and equipment	2,466	2,313	438
Unsettled repurchases of common stock	$ 0	$ 0	$ 1,995