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Summary of Significant Accounting Policies (Details) - USD ($)
3 Months Ended 6 Months Ended
Jun. 30, 2017
Mar. 31, 2017
Jun. 30, 2016
Jun. 30, 2017
Jun. 30, 2016
Dec. 31, 2016
Property and equipment            
Accumulated depreciation $ 58,220,000     $ 58,220,000   $ 57,114,000
Costs to remove long-lived assets   $ 286,000   286,000    
Depreciation $ 823,000   $ 867,000 $ 1,644,000 $ 1,763,000  
Track Related Assets            
Property and equipment            
Depreciation     $ 68,000   $ 159,000