Income Taxes (Details) (USD $)
In Thousands, unless otherwise specified
 12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Income before income taxes      
Income before income taxes $ 38,300 $ 35,565 $ 40,658
Provision for income taxes      
Federal 13,159 7,089 15,853
State 2,524 2,183 2,239
Canadian 2,127 1,724 1,578
Total current 17,810 10,996 19,670
Deferred taxes (2,679) 1,716 (3,607)
Total taxes on income 15,131 12,712 16,063
Tax rate reconciliation      
Statutory U.S. federal tax rate 35.00% 35.00% 35.00%
State income taxes, net of federal benefit 3.90% 3.60% 3.90%
Effect of Canadian income taxes (1.70%) (1.60%) (1.00%)
Nondeductible expenses 1.90% 1.90% 1.40%
ESOP dividend deduction (0.70%) (0.80%) (0.70%)
Audit settlements and uncertain tax adjustments 1.60% (2.20%) 1.80%
All other, net (0.50%) (0.20%) (0.90%)
Effective income tax rate 39.50% 35.70% 39.50%
Current deferred tax assets and liabilities, net      
Accrued compensation obligations 3,090 1,883  
Self-insurance accruals 8,107 7,693  
Prepaid expenses (3,160) (2,565)  
Other, net 1,102 908  
Deferred tax assets, current, gross 9,139 7,919  
Less deferred tax asset valuation allowance 212 204  
Net deferred income tax assets--current 8,927 7,715  
Noncurrent deferred tax assets and liabilities, net      
Deferred Tax Assets, Tax Deferred Expense, Reserves and Accruals, Self Insurance 12,554 12,129  
Accrued expenses and other liabilities 1,388 895  
Accrued stock compensation 1,642 1,550  
Defined benefit pension plans 4,573 1,873  
Foreign tax credit carryforward 768 768  
Other future deductible amounts, net 2,030 1,737  
Deferred tax assets, gross, noncurrent 22,955 18,952  
Less deferred tax asset valuation allowance 556 564  
Deferred tax assets, net of valuation allowance 22,399 18,388  
Intangibles 269 234  
Property and equipment 20,425 20,718  
Deferred tax liability, noncurrent 20,694 20,952  
Net deferred tax assets--noncurrent 1,705 0  
Net deferred tax liabilities--noncurrent 0 2,564  
Undistributed Earnings of Foreign Subsidiaries 30,459    
Unrecognized benefits and related interest and penalties      
Unrecognized tax benefits 1,949 1,221 2,638
Portion, if recognized, would reduce tax expense and effective tax rate 1,512 942  
Accrued interest on unrecognized tax benefits 77 41  
Accrued penalties on unrecognized benefits 0 0  
Reconciliation of unrecognized tax benefits      
Balance, beginning of year 1,221 2,638 1,825
Additions based on tax positions related to the current year 587 370 667
Additions for tax positions of prior years 234 133 149
Reductions for tax positions of prior years (79) (1,155) (3)
Reductions related to settlements with taxing authorities 0 (460) 0
Lapses in statutes of limitations (14) (305) 0
Balance, end of year 1,949 1,221 2,638
United States [Member]      
Income before income taxes      
Income before income taxes 30,380 29,203 35,414
Canada [Member]      
Income before income taxes      
Income before income taxes $ 7,920 $ 6,362 $ 5,244