Accounting Policies (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 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%
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
Required deposit equal to approximately one day of claims funding activity	6,500
Amount which plan costs were less than the net premiums paid and owed	13,300
Prepaid health insurance, current	4,300
Premiums owed to United	55,000
Benefits costs incurred (reduced) related to run-off	(800)	$ (5,500)
Workers' Compensation Costs [Abstract]
Company's maximum economic burden for the first layer of claims per occurrence	1,000				$ 1,500
Company's maximum aggregate economic burden for claims in excess of 1 million per policy year	6,000				$ 6,000
Decrease Increase in accrued workers' compensation costs for changes in estimated losses	$ 14,900	$ 13,200
U.S. Treasury rates that correspond with the weighted average estimated claim payout period (in hundredths)	1.50%	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	$ 8,373	$ 9,616
Present value discount, net of accretion	(1,309)	(442)
Paid claims	(14,370)	(13,246)
WorkersCompensationLiabilityNetOfAdminFeesCurrent	49,429	46,353
Long-term portion of accrued claims	182,888	190,336	192,694
Ending balance	232,317	236,689
Workers compensation administrative fees accrued	3,900
Undiscounted accrued workers' compensation costs	$ 248,000	253,200
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	$ 49,429	46,353	46,929	45,522
Deposits workers compensation	$ 190,756	193,067	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	$ 655,300		$ 490,500
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	1,577,837	1,286,835
Northeast [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	449,925	373,629
Southeast [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	202,201	156,260
Central [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	271,310	225,700
Southwest [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	308,838	256,979
West [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	330,771	261,354
Other Revenues [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	$ 14,792	$ 12,913