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Contract Services and Advanced Technology Costs (Narrative) (Details) - USD ($)
$ in Millions
 9 Months Ended 12 Months Ended
Sep. 30, 2017
Sep. 30, 2018
Sep. 30, 2017
Sep. 30, 2016
Contract monthly revenue     $ 2.0  
Contract revenue current work $ 24.2      
Contract revenue past work $ 8.1      
2018 ORNL Contract [Member] | Scenario, Forecast [Member]        
Contract value   $ 16.0    
2017 ORNL Contract [Member]        
Contract value     25.0  
Contract milestone payments     $ 1.0  
2016 ORNL Contract [Member]        
Contract monthly revenue       $ 2.7