Annual report pursuant to Section 13 and 15(d)

Accounting Policies (Details)

v3.8.0.1
Accounting Policies (Details)
$ in Thousands
 12 Months Ended
Dec. 31, 2017
USD ($)
Days
Dec. 31, 2016
USD ($)
Dec. 31, 2015
USD ($)
Accounting Policies [Line Items]      
Number of principal reporting segments 4    
Undistributed Earnings (Loss) Allocated to Participating Securities, Basic $ 700 $ 212 $ 369
Accounting Policies, Use of Estimates [Abstract]      
Minimum number of days past due for receivable reserve | Days 90    
Average monthly revenue adjustments $ 255    
Average monthly revenue $ 91,735    
Average monthly revenue adjustments as a percentage of monthly revenue 0.30%    
Number of days in revenue adjustment reserve, minimum | Days 35    
Number of days in revenue adjustment reserve, maximum | Days 65    
Self insurance limit on individual vehicle and general claims $ 1,000    
Self insurance limit on workers' compensation claims 350    
Self insurance limit on health insurance claims 225    
Self Insurance limit on Ohio workers' compensation insurance claims $ 500    
Accounting Policies, Cash and Cash Equivalents [Abstract]      
Maximum term for liquid investments to be considered cash equivalents, in months 3    
Accounting Policies, Property and Equipment [Abstract]      
Depreciation $ 30,862 28,088 26,252
Accounting Policies, Software Development [Abstract]      
Capitalized software development costs 19,567 16,268  
Capitalized computer software, accumulated amortization 10,874 10,716  
Capitalized Computer Software, Amortization 1,816 $ 1,658 $ 1,526
Black-Scholes option pricing model assumptions [Abstract]      
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification $ 545    
Software and Software Development Costs [Member]      
Accounting Policies, Property and Equipment [Abstract]      
Property and equipment, useful life 5 years    
Capitalized software future estimated amortization expense      
2018 $ 2,197    
2019 1,878    
2020 1,620    
2021 1,327    
2022 716    
Total $ 7,738    
Stock Option [Member]      
Accounting Policies, Share-based Payments [Abstract]      
Period from grant date of stock options to expiration (in years) 7 years    
Share-based awards, vesting period 3 years    
Black-Scholes option pricing model assumptions [Abstract]      
Expected dividend yield (in hundredths) 1.30% 1.00% 1.00%
Expected stock price volatility 28.50% 28.90% 33.30%
Weighted average risk-free interest rate 2.00% 1.30% 1.60%
Expected life of options (in years) 5 years 10 months 11 days 5 years 9 months 11 days 5 years 10 months 11 days
Key Employee Performance Share Based Plan [Member]      
Accounting Policies, Share-based Payments [Abstract]      
Share-based awards, vesting period 3 years    
Black-Scholes option pricing model assumptions [Abstract]      
Expected stock price volatility 24.70% 22.30% 23.50%
Weighted average risk-free interest rate 1.40% 0.80% 1.00%
Employee Stock Purchase Plan [Member]      
Black-Scholes option pricing model assumptions [Abstract]      
Percentage of share price for shares issued under the ESPP (in hundredths) 90.00%    
Purchase Period for Employee Stock Purchase Plan 6 months    
Number of large lump sum contributions related to ESPP stock purchases 2    
Expedited LTL [Member]      
Accounting Policies, Use of Estimates [Abstract]      
Reserve percentage for past due accounts receivable 50.00%    
Intermodal [Member]      
Accounting Policies, Use of Estimates [Abstract]      
Reserve percentage for past due accounts receivable 10.00%    
Pool Distribution [Member]      
Accounting Policies, Use of Estimates [Abstract]      
Reserve percentage for past due accounts receivable 25.00%    
Truckload Premium Services [Member]      
Accounting Policies, Use of Estimates [Abstract]      
Reserve percentage for past due accounts receivable 50.00%    
Minimum [Member] | Building [Member]      
Accounting Policies, Property and Equipment [Abstract]      
Property and equipment, useful life 30 years    
Minimum [Member] | Equipment [Member]      
Accounting Policies, Property and Equipment [Abstract]      
Property and equipment, useful life 3 years    
Maximum [Member] | Building [Member]      
Accounting Policies, Property and Equipment [Abstract]      
Property and equipment, useful life 40 years    
Maximum [Member] | Equipment [Member]      
Accounting Policies, Property and Equipment [Abstract]      
Property and equipment, useful life 10 years    
Accounting Standards Update 2014-09 [Member]      
Black-Scholes option pricing model assumptions [Abstract]      
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification $ 66,000 $ 47,000