Accounting Policies (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 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	41,800		41,800
Prepaid health insurance, current	32,800		32,800
Premiums owed to United	55,900		55,900
Benefits costs incurred (reduced) related to run-off	(10,200)	$ (5,700)	(10,200)	$ (5,700)
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			$ 26,800	$ 23,000
U.S. Treasury rates that correspond with the weighted average estimated claim payout period (in hundredths)			2.00%	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			$ 18,780	$ 20,559
Present value discount, net of accretion			(3,501)	407
Paid claims			(27,899)	(22,904)
WorkersCompensationLiabilityNetOfAdminFeesCurrent	53,317	46,120	53,317	46,120
Long-term portion of accrued claims	173,686	192,703	173,686	192,703	192,694
Ending balance	227,003	238,823	227,003	238,823
Workers compensation administrative fees accrued	4,800		4,800
Undiscounted accrued workers' compensation costs			$ 243,900	254,800
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	53,329	46,128	$ 53,329	46,128	46,929	45,522
Deposits workers compensation	166,077	203,612	$ 166,077	203,612	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	674,400		$ 674,400		$ 490,500
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	1,432,107	1,185,371	3,009,944	2,472,206
ReturnOfExcessClaimFunds			30,200
Northeast [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	388,680	329,016	838,602	702,645
Southeast [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	192,782	150,810	394,985	307,070
Central [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	252,039	206,084	523,350	431,784
Southwest [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	279,936	238,368	588,774	495,348
West [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	304,380	247,184	635,152	508,538
Other Revenues [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	$ 14,290	$ 13,909	$ 29,081	$ 26,821