CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Income Statement [Abstract]
Revenues(1)	[1]	$ 5,938,818	$ 4,973,070	$ 4,287,004
Payroll taxes, benefits and workers’ compensation costs		4,927,585	4,152,968	3,480,150
Gross profit		1,011,233	820,102	806,854
Salaries, wages and payroll taxes		430,945	379,171	353,273
Stock-based compensation		50,080	40,623	60,145
Commissions		45,672	34,922	32,835
Advertising		37,503	29,097	21,556
General and administrative expenses		156,134	124,413	113,167
Depreciation and amortization		40,660	38,547	31,189
Total operating expenses		760,994	646,773	612,165
Operating income		250,239	173,329	194,689
Other income (expense):
Interest income		9,393	2,447	2,597
Interest expense		(14,207)	(7,458)	(8,016)
Income before income tax expense		245,425	168,318	189,270
Income tax expense		66,075	44,238	51,033
Net income		$ 179,350	$ 124,080	$ 138,237
Basic net income per share of common stock (in dollars per share)		$ 4.70	$ 3.22	$ 3.57
Diluted net income per share of common stock (in dollars per share)		$ 4.64	$ 3.18	$ 3.54
Gross billings		$ 40,126,910	$ 33,318,693	$ 28,168,611
Worksite employee payroll cost		$ 34,188,092	$ 28,345,623	$ 23,881,607

[1] Revenues are comprised of gross billings less worksite employee (“WSEE”) payroll costs as follows: Year ended December 31, (in thousands) 202220212020 Gross billings $40,126,910 $33,318,693 $28,168,611  Less: WSEE payroll cost 34,188,092 28,345,623 23,881,607  Revenues $5,938,818 $4,973,070 $4,287,004