Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current provision (benefit)
Federal	$ 21,509	$ 4,726	$ 26,948
State	3,371	5,423	3,640
Foreign	(188)	92	362
Total	24,692	10,241	30,950
Deferred provision (benefit)
Federal	1,958	11,560	(7,099)
State	1,219	(727)	155
Foreign	(36)	72	(60)
Total	3,141	10,905	(7,004)
Change in valuation allowance	600
Total	$ 28,433	$ 21,146	$ 23,946
Reconciliation of income tax expense compared to the amount of income tax expense that would result by applying U.S. federal statutory income tax rate to pre-tax income
U.S. federal statutory income tax rate (as a percent)	35.00%	35.00%	35.00%
State taxes, net of federal income tax impact (as a percent)	2.90%	6.40%	4.20%
Foreign tax credit (as a percent)	(0.00%)	(0.40%)	(0.50%)
Canadian income tax (benefit) provision (as a percent)	(0.20%)	0.40%	0.50%
Domestic production activities deduction (as a percent)	(2.30%)	(1.10%)	(3.90%)
Nondeductible meals & entertainment (as a percent)	2.80%	5.40%	5.10%
Other items (as a percent)	(0.70%)	(1.50%)	(1.00%)
Effective tax rate excluding the impact of the Tax Act and income attributable to noncontrolling interests (as a percent)	37.50%	44.20%	39.40%
Deferred tax liability remeasurement benefit from the Tax Act	(9.30%)	0.00%	0.00%
Effective tax rate excluding income attributable to noncontrolling interests (as a percent)	28.20%	44.20%	39.40%
Impact of income from noncontrolling interests on effective tax rate (as a percent)	(1.20%)	(0.90%)	(0.20%)
Effective tax rate (as a percent)	27.00%	43.30%	39.20%
Estimated net tax benefit of Tax Act	$ 9,400
Deferred tax assets:
Accrued compensation	3,323	$ 5,804
Accrued workers compensation	6,197	9,855
Capital loss carryforward		1,077
Foreign tax credit	1,456	1,349
Insurance reserves	2,544	3,248
Loss reserves	2,215	4,841
Pension liability		1,979
State income taxes	2,233	2,011
Other	202	288
Total deferred tax assets	18,170	30,452
Deferred tax liabilities
Depreciation and amortization	(30,555)	(38,327)
Prepaid expense and other	(586)	(1,955)
Total deferred tax liabilities	(31,141)	(40,282)
Valuation allowance	(600)
Net deferred tax liabilities	$ (13,571)	$ (9,830)
Minimum period of statute of limitations of state and foreign jurisdictions	3 years
Maximum period of statute of limitations of state and foreign jurisdictions	5 years
Reconciliation and aggregate changes for unrecognized tax benefits
Beginning balance			$ 456
Increases in balances for tax positions taken during the current year	$ 592
Settlements and effective settlements with tax authorities			$ (456)
Total	592
State
Deferred tax liabilities
Net operating loss	800
Tax credit carryforward	1,100
Foreign
Deferred tax liabilities
Tax credit carryforward	1,500
Minimum
Deferred tax liabilities
Reasonably possible decrease in unrecognized tax benefits	0
Maximum
Deferred tax liabilities
Reasonably possible decrease in unrecognized tax benefits	$ 100