CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Assets
Cash and cash equivalents	$ 732,828	$ 575,812
Restricted cash	49,779	46,929
Marketable securities	33,068	31,791
Accounts receivable, net	622,764	513,306
Prepaid insurance	11,706	11,285
Income taxes receivable	0	12,413
Other current assets	61,728	53,312
Total current assets	1,511,873	1,244,848
Property and equipment, net	199,992	210,723
Right-of-use “ROU” leased assets	56,532	62,830
Deposits and prepaid health insurance	213,270	201,927
Goodwill and other intangible assets, net	12,707	12,707
Deferred income taxes, net	15,533	4,892
Other assets	29,354	15,158
Total assets	2,039,261	1,753,085
Liabilities and stockholders’ equity
Accounts payable	7,732	6,412
Payroll taxes and other payroll deductions payable	556,085	467,892
Accrued worksite employee payroll cost	513,397	409,653
Accrued health insurance costs	53,402	50,001
Accrued workers’ compensation costs	53,485	50,534
Accrued corporate payroll and commissions	89,147	74,778
Other accrued liabilities	80,122	69,303
Total current liabilities	1,353,370	1,128,573
Accrued workers’ compensation costs, net of current	179,629	192,694
Long-term debt	369,400	369,400
Operating lease liabilities, net of current	55,587	64,192
Total noncurrent liabilities	604,616	626,286
Commitments and contingencies
Preferred stock, issued (in shares)	0	0
Preferred stock, par value (in dollars per share)	$ 0.01
Stockholders' Equity Attributable to Parent [Abstract]
Preferred stock ($0.01 per share par value; 20,000 shares authorized; no shares issued and outstanding)	$ 0	$ 0
Common stock ($0.01 per share par value; 120,000 shares authorized; 55,489 shares issued and 37,881 shares and 38,330 shares outstanding, respectively)	555	555
Additional paid-in capital	151,144	109,179
Treasury stock, at cost (17,608 and 17,159 shares held in treasury, respectively)	(725,532)	(665,089)
Accumulated other comprehensive income (loss), net of tax	(82)	(9)
Retained earnings	655,190	553,590
Retained earnings	81,275	(1,774)
Total liabilities and stockholders’ equity	$ 2,039,261	$ 1,753,085
Stockholders' Equity, Number of Shares, Par Value and Other Disclosures [Abstract]
Preferred stock, authorized (in shares)	20,000,000
Common stock, par value (in dollars per share)	$ 0.01
Common stock, authorized (in shares)	120,000,000
Common stock, issued (in shares)	55,489,000	55,489,000
Common Stock, Shares, Outstanding	37,881,000	38,330,000
Treasury stock, shares (in shares)	17,608,000	17,159,000