CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
Operating activities
Net income	$ 68,688	$ 23,859
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	16,496	17,919
Stock-based compensation	13,706	13,905
Changes in operating assets and liabilities:
Restricted cash and cash equivalents	(31,982)	(21,041)
Prepaid income taxes	27,665	(2,863)
Prepaid expenses and other current assets	(2,601)	(5,033)
Workers' compensation collateral receivable	4,820	(10,599)
Other assets	91	238
Accounts payable	4,002	2,488
Accrued corporate wages and other current liabilities	8,299	(719)
Workers' compensation loss reserves and other non-current liabilities	(5,061)	25,792
Worksite employee related assets	382,875	425,815
Worksite employee related liabilities	(382,885)	(426,094)
Net cash provided by operating activities	104,113	43,667
Investing activities
Acquisitions of businesses	0	(300)
Purchases of marketable securities	0	(14,959)
Proceeds from maturity of marketable securities	11,469	24,998
Acquisitions of property and equipment	(20,725)	(16,714)
Net cash used in investing activities	(9,256)	(6,975)
Financing activities
Repurchase of common stock	(29,510)	(16,459)
Proceeds from issuance of common stock on exercised options	5,586	2,220
Proceeds from issuance of common stock on employee stock purchase plan	2,441	2,304
Awards effectively repurchased for required employee withholding taxes	(4,507)	(1,485)
Repayment of notes and capital leases payable	(19,151)	(22,810)
Net cash used in financing activities	(45,141)	(36,230)
Effect of exchange rate changes on cash and cash equivalents	163	24
Net increase in cash and cash equivalents	49,879	486
Cash and cash equivalents at beginning of period	184,004	166,178
Cash and cash equivalents at end of period	233,883	166,664
Supplemental disclosures of cash flow information
Interest paid	8,006	8,091
Income taxes paid (refunded), net	(169)	21,374
Supplemental schedule of noncash investing and financing activities
Payable for purchase of property and equipment	$ 1,580	$ 1,581