CONSOLIDATED STATEMENTS OF CASH FLOWS (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Cash flows from operating activities:
Net income	$ 40,402	$ 30,470	$ 22,440
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	18,183	15,218	14,950
Loss on exchange of assets	0	4,408	0
Impairment charge	4,191	0	0
Amortization of marketable securities	2,295	2,172	1,650
Stock-based compensation	9,814	8,601	8,126
Deferred income taxes	(5,743)	(46)	1,179
Changes in operating assets and liabilities, net of acquisitions:
Restricted cash	(2,412)	(3,533)	(4,768)
Accounts receivable	(19,453)	(28,826)	(18,874)
Prepaid insurance	5,680	3,678	(10,494)
Other current assets	1,837	(2,862)	(2,141)
Other assets	(12,924)	(652)	4,180
Accounts payable	(1,425)	1,776	1,136
Payroll taxes and other payroll deductions payable	9,922	23,556	17,499
Accrued worksite employee payroll expense	19,753	20,620	16,559
Accrued health insurance costs	4,515	(5,992)	9,045
Accrued workers' compensation costs	7,418	8,791	8,748
Accrued corporate payroll, commissions and other accrued liabilities	2,353	(1,871)	9,556
Income taxes payable/receivable	6,392	(1,597)	49
Total adjustments	50,396	43,441	56,400
Net cash provided by operating activities	90,798	73,911	78,840
Marketable securities:
Purchases	(30,680)	(51,397)	(60,003)
Proceeds from maturities	32,619	31,706	18,301
Proceeds from dispositions	35,891	3,907	2,748
Investments and acquisitions, net of cash acquired	(2,410)	(14,555)	(12,918)
Property and equipment:
Purchases	(17,631)	(31,440)	(6,764)
Proceeds from dispositions	69	82	54
Net cash provided by (used in) investing activities	17,858	(61,697)	(58,582)
Cash flows from financing activities:
Purchase of treasury stock	(13,773)	(25,079)	(7,852)
Repurchase of common stock	(3,162)	0	0
Dividends paid	(42,728)	(15,742)	(13,527)
Proceeds from the exercise of stock options	2,249	3,956	7,183
Income tax benefit from stock-based compensation	2,316	2,166	860
Other	(222)	(1,136)	822
Net cash used in financing activities	(55,320)	(35,835)	(12,514)
Net increase (decrease) in cash and cash equivalents	53,336	(23,621)	7,744
Cash and cash equivalents at beginning of year	211,208	234,829	227,085
Cash and cash equivalents at end of year	264,544	211,208	234,829
Supplemental disclosures:
Cash paid for income taxes	$ 24,924	$ 19,782	$ 13,492