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
 12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]        
SEC Schedule, 12-09, Valuation Allowances and Reserves, Amount $ 2,496 $ 2,476 $ 3,366 $ 1,996
Valuation Allowances and Reserves, Charged to Cost and Expense 761 174 1,892  
SEC Schedule, 12-09, Valuation Allowances and Reserves, Deduction 4,083 4,692 3,577  
SEC Schedule, 12-09, Allowance, Credit Loss [Member]        
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]        
SEC Schedule, 12-09, Valuation Allowances and Reserves, Amount 1,344 1,309 2,542 1,309
Valuation Allowances and Reserves, Charged to Cost and Expense 761 139 1,814  
SEC Schedule, 12-09, Valuation Allowances and Reserves, Deduction [1] 726 1,372 581  
Allowance for revenue adjustments [Member]        
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]        
SEC Schedule, 12-09, Valuation Allowances and Reserves, Amount 757 772 [2] 464 [2] 405 [2]
SEC Schedule, 12-09, Valuation Allowances and Reserves, Additions, Charge to Other Account 3,342 3,628 3,055  
SEC Schedule, 12-09, Valuation Allowances and Reserves, Deduction [3] 3,357 3,320 2,996  
SEC Schedule, 12-09, Valuation Allowance, Deferred Tax Asset [Member]        
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]        
SEC Schedule, 12-09, Valuation Allowances and Reserves, Amount 395 395 360 $ 282
Valuation Allowances and Reserves, Charged to Cost and Expense $ 0 $ 35 $ 78  
[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