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Accounting Policies (Details) - USD ($) $ in Thousands | 3 Months Ended |  |
--- | --- | --- | ---
Mar. 31, 2019 | Mar. 31, 2018 | Dec. 31, 2018 | Dec. 31, 2017
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 | 6,000 |  |  |
Amount which plan costs were less than the net premiums paid and owed | 19,500 |  |  |
Prepaid health insurance, current | 10,500 |  |  |
Premiums owed to United | 40,600 |  |  |
Benefits costs incurred (reduced) related to run-off |  | $ 3,800 |  |
Workers' Compensation Costs [Abstract] |  |  |  |
Company's maximum economic burden for the first layer of claims per occurrence | 1,000 |  |  |
Company's maximum aggregate economic burden for claims in excess of 1 million per policy year | 6,000 |  |  |
Decrease Increase in accrued workers' compensation costs for changes in estimated losses | $ 7,800 | $ 5,700 |  |
U.S. Treasury rates that correspond with the weighted average estimated claim payout period (in hundredths) | 2.50% | 2.50% |  |
Incurred but not paid workers compensation liabilities [Abstract] |  |  |  |
Beginning balance, January 1, | $ 229,639 | $ 207,630 |  |
Accrued claims | 15,787 | 16,903 |  |
Present value discount | (1,689) | (1,692) |  |
Paid claims | (12,409) | (9,931) |  |
Ending balance | 231,328 | 212,910 |  |
Current portion of accrued claims | 44,704 | 41,137 |  |
Long-term portion of accrued claims | 186,624 | 171,773 | 187,412 |
Workers compensation administrative fees accrued | 3,300 |  |  |
Undiscounted accrued workers' compensation costs | $ 250,200 | 226,400 |  |
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 | $ 44,705 | 41,137 | 42,227 | $ 41,137
Deposits workers compensation | $ 170,905 | 160,840 | 166,474 | $ 154,215
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 |  |  |
Unbilled | $ 411,742 |  | $ 385,567 |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer, Excluding Assessed Tax | 1,153,010 | 1,014,372 |  |
Northeast [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer, Excluding Assessed Tax | 310,945 | 272,363 |  |
Southeast [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer, Excluding Assessed Tax | 129,906 | 115,188 |  |
Central [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer, Excluding Assessed Tax | 195,753 | 168,068 |  |
Southwest [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer, Excluding Assessed Tax | 269,832 | 232,866 |  |
West [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer, Excluding Assessed Tax | 233,204 | 212,619 |  |
Other Revenues [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer, Excluding Assessed Tax | $ 13,370 | $ 13,268 |  |

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