Property and Equipment (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Total property and equipment	$ 739,278	$ 810,727
Accumulated depreciation	(369,415)	(413,802)
Property and equipment — net	369,863	396,925
Land [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment	9,992	9,992
Building and Improvements [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment	5,071	5,071
Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment	14,087	12,453
Operating Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment	$ 710,128	$ 783,211