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, 2016
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Valuation and Qualifying Accounts Disclosure [Line Items]        
Valuation Allowances and Reserves, Balance $ 1,996 $ 2,689 $ 2,836 $ 2,153
Valuation Allowances and Reserves, Charged to Cost and Expense 2,276 4,837 2,745  
Valuation Allowances and Reserves, Deductions 2,969 4,984 2,062  
Allowance for Doubtful Accounts [Member]        
Valuation and Qualifying Accounts Disclosure [Line Items]        
Valuation Allowances and Reserves, Balance 1,309 1,310 2,155 1,583
Valuation Allowances and Reserves, Charged to Cost and Expense 258 33 241  
Valuation Allowances and Reserves, Deductions [1] 259 878 (331)  
Allowance for revenue adjustments [Member]        
Valuation and Qualifying Accounts Disclosure [Line Items]        
Valuation Allowances and Reserves, Balance [2] 405 1,095 408 336
Valuation Allowances and Reserves, Charged to Cost and Expense [2] 2,020 4,793 2,465  
Valuation Allowances and Reserves, Deductions [2],[3] 2,710 4,106 2,393  
Valuation Allowance of Deferred Tax Assets [Member]        
Valuation and Qualifying Accounts Disclosure [Line Items]        
Valuation Allowances and Reserves, Balance 282 284 273 $ 234
Valuation Allowances and Reserves, Charged to Cost and Expense $ (2) $ 11 $ 39  
[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