Annual report pursuant to Section 13 and 15(d)

Schedule of Equity Method Investment, Financial Information, Statement of Operations (Details)

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Schedule of Equity Method Investment, Financial Information, Statement of Operations (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Dart Holding Company Ltd.      
Schedule of Equity Method Investments [Line Items]      
Operating revenues $ 42,891 $ 40,930 $ 33,190
Operating and administrative 35,983 32,878 32,869
Depreciation and amortization 1,603 3,161 4,224
Total Costs and Expenses 37,586 36,039 37,093
Operating income 5,305 4,891 (3,903)
Net income 3,603 2,657 (3,150)
Other Investments      
Schedule of Equity Method Investments [Line Items]      
Operating revenues 581 694 622
Operating and administrative 367 338 685
Depreciation and amortization 503 519 740
Total Costs and Expenses 870 857 1,425
Operating income (289) (163) (803)
Net income $ (527) $ (409) $ (1,064)