Annual report pursuant to Section 13 and 15(d)

Significant Accounting Policies (Narrative) (Details)

v3.6.0.2
Significant Accounting Policies (Narrative) (Details) - USD ($)
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Significant Accounting Policies [Line Items]      
Depreciation expenses including capital leases $ 189,600,000 $ 164,800,000 $ 145,800,000
Self-insurance reserve 125,800,000 119,200,000  
Long-term portions of self insurance reserve 78,400,000 74,300,000  
Advertising expense 20,500,000 22,900,000 $ 19,300,000
Debt and Capital Lease Obligations 104,975,000 133,805,000  
Long-term Debt, Fair Value 108,300,000 $ 139,100,000  
Group Health Claims [Member]      
Significant Accounting Policies [Line Items]      
Insurance maximum, per occurrence 800,000    
Workers Compensation Claims [Member]      
Significant Accounting Policies [Line Items]      
Insurance maximum, per occurrence 1,000,000    
Cargo Loss And Damage Claims [Member]      
Significant Accounting Policies [Line Items]      
Insurance maximum, per occurrence 100,000    
Bodily Injury And Property Damage [Member]      
Significant Accounting Policies [Line Items]      
Insurance maximum, per occurrence 2,750,000    
Corridor Deductible 2,500,000    
Insurance Layer to Meet Corridor Deductible 5,000,000    
2016 Share Repurchase Program [Member]      
Significant Accounting Policies [Line Items]      
Stock Repurchase Program, Authorized Amount 250,000,000    
Stock Repurchase Program, Remaining Authorized Repurchase Amount 200,000,000    
2014 Share Repurchase Program [Member]      
Significant Accounting Policies [Line Items]      
Stock Repurchase Program, Authorized Amount $ 200,000,000