CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Operating activities
Net income	$ 111,524	$ 38,440
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	26,177	27,810
Stock-based compensation	21,406	20,169
Changes in operating assets and liabilities:
Restricted cash and cash equivalents	(45,570)	(31,409)
Prepaid income taxes	42,448	386
Prepaid expenses and other current assets	(961)	(5,253)
Workers' compensation collateral receivable	(8,048)	(11,374)
Other assets	925	438
Accounts payable	5,505	4,538
Accrued corporate wages and other current liabilities	2,331	4,548
Workers' compensation loss reserves and other non-current liabilities	3,574	33,510
Worksite employee related assets	340,767	525,841
Worksite employee related liabilities	(341,127)	(526,945)
Net cash provided by operating activities	158,951	80,699
Investing activities
Acquisitions of businesses	0	(300)
Purchases of marketable securities	0	(14,959)
Proceeds from maturity of marketable securities	14,447	25,790
Acquisitions of property and equipment	(29,210)	(27,942)
Net cash used in investing activities	(14,763)	(17,411)
Financing activities
Repurchase of common stock	(39,347)	(43,747)
Proceeds from issuance of common stock on exercised options	8,678	3,584
Proceeds from issuance of common stock on employee stock purchase plan	2,441	2,304
Awards effectively repurchased for required employee withholding taxes	(8,100)	(2,672)
Proceeds from issuance of notes payable	0	57,978
Payments for extinguishment of debt	0	(57,563)
Repayment of notes and capital leases payable	(28,735)	(27,506)
Payment of debt issuance costs	0	(1,376)
Net cash used in financing activities	(65,063)	(68,998)
Effect of exchange rate changes on cash and cash equivalents	398	90
Net increase in cash and cash equivalents	79,523	(5,620)
Cash and cash equivalents at beginning of period	184,004	166,178
Cash and cash equivalents at end of period	263,527	160,558
Supplemental disclosures of cash flow information
Interest paid	12,186	11,651
Income taxes paid (refunded), net	(138)	27,650
Supplemental schedule of noncash investing and financing activities
Payable for purchase of property and equipment	$ 2,450	$ 1,363