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, 2018
Dec. 31, 2017
Dec. 31, 2016
Dart Holding Company Ltd.      
Schedule of Equity Method Investments [Line Items]      
Operating revenues $ 45,602 $ 42,891 $ 40,930
Operating and administrative 36,592 35,983 32,878
Depreciation and amortization 1,754 1,603 3,161
Total costs and expenses 38,346 37,586 36,039
Operating income 7,256 5,305 4,891
Net income 4,912 3,603 2,657
Other Investments      
Schedule of Equity Method Investments [Line Items]      
Operating revenues 170 581 694
Operating and administrative 63 367 338
Depreciation and amortization 377 503 519
Total costs and expenses 440 870 857
Operating income (270) (289) (163)
Net income $ (442) $ (527) $ (409)