Accounting Policies (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021	Dec. 31, 2021	Dec. 31, 2020	Oct. 01, 2019
Health Insurance Costs [Abstract]
Percentage of our health insurance coverage provided by United	87.00%		87.00%
Number of days in advance of the beginning of a reporting quarter United establishes cash funding rates			90 days
Required accumulated cash surplus	$ 9,000		$ 9,000		$ 9,000
Required deposit equal to approximately one day of claims funding activity	6,500		6,500
Amount which plan costs were less than the net premiums paid and owed	25,200		25,200
Prepaid health insurance, current	16,200		16,200
Premiums owed to United	57,600		57,600
Benefits costs incurred (reduced) related to run-off	(12,800)	$ (4,500)	(12,800)	$ (4,500)
Workers' Compensation Costs [Abstract]
Company's maximum economic burden for the first layer of claims per occurrence	1,000		1,000				$ 1,500
Company's maximum aggregate economic burden for claims in excess of 1 million per policy year	6,000		6,000				$ 6,000
Decrease Increase in accrued workers' compensation costs for changes in estimated losses			$ (35,300)	$ (31,400)
U.S. Treasury rates that correspond with the weighted average estimated claim payout period (in hundredths)			2.50%	0.50%
Incurred but not paid workers compensation liabilities [Abstract]
Liability for Unpaid Claims and Claims Adjustment Expense, Adjustments					239,623	$ 240,761
Workers' Compensation Expense			$ 33,467	$ 34,349
Present value discount, net of accretion			(6,485)	476
Paid claims			(40,112)	(36,580)
WorkersCompensationLiabilityNetOfAdminFeesCurrent	51,829	47,813	51,829	47,813
Long-term portion of accrued claims	174,664	191,193	174,664	191,193	192,694
Ending balance	226,493	239,006	226,493	239,006
Workers compensation administrative fees accrued	5,200		5,200
Undiscounted accrued workers' compensation costs			$ 245,500	254,500
Time period incurred claims expected to be paid recorded as restricted cash			1 year
Time period incurred claims expected to be paid, included in deposits, a long-term asset			Greater than 1 year
Restricted cash	51,829	47,813	$ 51,829	47,813	46,929	45,522
Deposits workers compensation	179,014	208,236	$ 179,014	208,236	185,027	$ 186,331
Time period estimate of incurred claim costs to be paid included in short-term liabilities			1 year
Time period incurred claims expected to be paid, included in long-term liabilities			Greater than 1 year
Revenue from Contract with Customer [Abstract]
Unbilled	547,600		$ 547,600		$ 490,500
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	1,439,160	1,209,628	4,449,104	3,681,834
ReturnOfExcessClaimFunds			30,200
Northeast [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	385,541	332,587	1,224,142	1,035,233
Southeast [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	197,131	155,555	592,116	462,625
Central [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	256,150	211,315	779,500	643,100
Southwest [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	280,299	241,473	869,073	736,820
West [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	305,465	253,562	940,617	762,100
Other Revenues [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	$ 14,574	$ 15,136	$ 43,656	$ 41,956