Schedule of Equity Method Investment, Financial Information, Statement of Operations (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Dart Holding Company Ltd.
Schedule of Equity Method Investments [Line Items]
Operating revenues	$ 45,602	$ 42,891
Operating and administrative	36,592	35,983
Depreciation and amortization	1,754	1,603
Total costs and expenses	38,346	37,586
Operating income	7,256	5,305
Net income	4,912	3,603
Other Investments
Schedule of Equity Method Investments [Line Items]
Operating revenues	170	581
Operating and administrative	63	367
Depreciation and amortization	377	503
Total costs and expenses	440	870
Operating income	(270)	(289)
Net income	$ (442)	$ (527)