CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Cash flows from operating activities
Net income	$ 179,350	$ 124,080	$ 138,237
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	40,660	38,547	31,189
Amortization of marketable securities	843	884	783
Stock-based compensation	50,080	40,623	60,145
Deferred income taxes	(10,641)	4,711	(5,647)
Changes in operating assets and liabilities:
Accounts receivable	(109,458)	(120,560)	73,033
Prepaid insurance	(421)	(1,121)	254
Other current assets	(5,206)	(13,851)	4,032
Other assets and ROU assets	1,757	4,356	15,725
Accounts payable	1,320	209	1,638
Payroll taxes and other payroll deductions payable	88,193	89,932	100,712
Accrued worksite employee payroll expense	103,744	74,817	(67,023)
Accrued health insurance costs	3,401	17,316	11,505
Accrued workers’ compensation costs	(10,114)	(197)	(3,052)
Accrued corporate payroll, commissions and other accrued liabilities	(5,179)	14,716	(20,763)
Income taxes payable/receivable	19,362	(14,307)	5,585
Total adjustments	168,341	136,075	208,116
Net cash provided by operating activities	347,691	260,155	346,353
Marketable securities:
Purchases	(46,748)	(58,202)	(50,624)
Proceeds from maturities	44,955	60,045	49,635
Proceeds from dispositions	0	0	484
Property and equipment purchases	(30,329)	(32,856)	(98,116)
Net cash used in investing activities	(32,122)	(31,013)	(98,621)
Cash flows from financing activities
Purchase of treasury stock	73,285	69,725	99,415
Dividends paid	(76,592)	(144,179)	(61,869)
Borrowings under long-term debt agreement	0	0	100,000
Other	8,727	5,831	7,701
Net cash used in financing activities	(141,150)	(208,073)	(53,583)
Net increase in cash, cash equivalents, restricted cash and funds held for clients	174,419	21,069	194,149
Cash, cash equivalents, restricted cash and funds held for clients at beginning of year		786,699	592,550
Cash, cash equivalents, restricted cash and funds held for clients at end of year	1,013,919		786,699
Supplemental disclosures of cash flow information
Income taxes, net	57,354	53,835	51,097
Cash paid for interest	13,402	7,268	8,977
ROU assets obtained in exchange for lease obligations	9,736	19,572	$ 22,770
Reclassification, Other [Member]
Cash flows from financing activities
Cash, cash equivalents, restricted cash and funds held for clients at beginning of year	839,500
Cash, cash equivalents, restricted cash and funds held for clients at end of year		839,500
Previously Reported [Member]
Cash flows from financing activities
Cash, cash equivalents, restricted cash and funds held for clients at beginning of year	$ 807,768
Cash, cash equivalents, restricted cash and funds held for clients at end of year		$ 807,768