CONSOLIDATED STATEMENTS OF OPERATIONS (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Income Statement [Abstract]
Revenues(1)	$ 1,432,107	$ 1,185,371	$ 3,009,944	$ 2,472,206
Payroll taxes, benefits and workers’ compensation costs	1,192,239	985,817	2,484,302	2,021,207
Gross profit	239,868	199,554	525,642	450,999
Salaries, wages and payroll taxes	106,522	94,362	213,961	197,437
Stock-based compensation	15,631	13,781	25,477	25,603
Commissions	10,743	8,251	21,053	15,970
Advertising	12,427	8,975	21,022	14,297
General and administrative expenses	36,095	29,211	77,100	60,847
Depreciation and amortization	10,100	9,751	20,284	17,798
Total operating expenses	191,518	164,331	378,897	331,952
Operating Income (Loss), Total	48,350	35,223	146,745	119,047
Other income (expense):
Interest income	945	1,436	1,093	1,979
Interest expense	(2,691)	(1,975)	(4,616)	(3,574)
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest, Total	46,604	34,684	143,222	117,452
Income tax expense	13,005	9,530	39,739	30,376
Net income	33,599	25,154	103,483	87,076
Less distributed and undistributed earnings allocated to participating securities	(1)	(37)	(31)	(193)
Net income allocated to common shares	$ 33,598	$ 25,117	$ 103,452	$ 86,883
Basic net income per share of common stock (in dollars per share)	$ 0.88	$ 0.65	$ 2.70	$ 2.26
Diluted net income per share of common stock (in dollars per share)	$ 0.87	$ 0.65	$ 2.68	$ 2.24
Revenue Composition [Abstract]
Gross billings	$ 9,224,643	$ 7,637,851	$ 19,582,548	$ 15,688,273
Worksite employee payroll cost	7,792,536	6,452,480	16,572,604	13,216,067
Revenues(1)	$ 1,432,107	$ 1,185,371	$ 3,009,944	$ 2,472,206