Annual report pursuant to Section 13 and 15(d)

Schedule II - Valuation and Qualifying Accounts (Details)

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Schedule II - Valuation and Qualifying Accounts (Details) (USD $)
In Thousands, unless otherwise specified
 12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Dec. 31, 2009
Valuation and Qualifying Accounts Disclosure [Line Items]        
Valuation Allowances and Reserves, Balance $ 1,763 $ 1,851 $ 2,331 $ 2,378
Valuation Allowances and Reserves, Charged to Cost and Expense 2,173 1,747 1,413  
Valuation Allowances and Reserves, Deductions 2,261 2,227 1,460  
Allowance for Doubtful Accounts [Member]
        
Valuation and Qualifying Accounts Disclosure [Line Items]        
Valuation Allowances and Reserves, Balance 1,149 1,219 1,619 1,457
Valuation Allowances and Reserves, Charged to Cost and Expense 199 (217) (52)  
Valuation Allowances and Reserves, Deductions 269 [1] 183 [1] (214) [1]  
Allowance for revenue adjustments [Member]
        
Valuation and Qualifying Accounts Disclosure [Line Items]        
Valuation Allowances and Reserves, Balance 295 [2] 284 [2] 377 [2] 462 [2]
Valuation Allowances and Reserves, Charged to Cost and Expense 2,003 [2] 1,951 [2] 1,589 [2]  
Valuation Allowances and Reserves, Deductions 1,992 [2],[3] 2,044 [2],[3] 1,674 [2],[3]  
Valuation Allowance of Deferred Tax Assets [Member]
        
Valuation and Qualifying Accounts Disclosure [Line Items]        
Valuation Allowances and Reserves, Balance 319 348 335 459
Valuation Allowances and Reserves, Charged to Cost and Expense $ (29) $ 13 $ (124)  
[1] Represents uncollectible accounts written off, net of recoveries
[2] Represents an allowance for adjustments to accounts receivable due to disputed rates, accessorial charges and other aspects of previously billed shipments.
[3] Represents adjustments to billed accounts receivable