CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Cash Flows from Operating Activities:
Net income	$ 29,092	$ 22,391
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	14,413	14,475
Stock-based compensation	4,891	5,570
Provision for accounts receivable allowances	483	2,807
Workers’ compensation provision	813	645
Other	1,236	2,990
Changes in operating assets and liabilities:
Accounts receivable	(13,526)	(10,154)
Prepaid expenses and income taxes	8,218	(457)
Accounts payable	5,825	712
Accrued payroll and contract professional pay	6,473	144
Income taxes payable	(448)	11,226
Workers’ compensation loss reserves	(747)	(493)
Other	(1,990)	(6,056)
Net Cash Provided by Operating Activities	54,733	43,800
Cash Flows from Investing Activities:
Cash paid for property and equipment	(6,198)	(6,792)
Other	(20)	17
Net cash used in investing activities	(6,218)	(6,775)
Cash Flows from Financing Activities:
Principal payments of long-term debt	(10,000)	(26,000)
Proceeds from long-term debt	0	2,000
Payments of Debt Issuance Costs	0	2,403
Proceeds from option exercises and employee stock purchase plan	4,388	4,106
Payment of employment taxes related to release of restricted stock awards	(2,055)	(5,782)
Repurchase of common stock	0	(12,136)
Net Cash Used in Financing Activities	(7,667)	(40,215)
Effect of exchange rate changes on cash and cash equivalents	385	151
Net Increase (Decrease) in Cash and Cash Equivalents	41,233	(3,039)
Cash and Cash Equivalents at Beginning of Year	36,667	27,044
Cash and Cash Equivalents at End of Period	77,900	24,005
Supplemental Disclosure of Cash Flow Information:
Income taxes	1,145	936
Interest	5,329	7,492
Supplemental Disclosure of Non-Cash Transactions:
Unpaid portion of additions to property and equipment	$ 1,985	$ 2,332