Contract Services and Advanced Technology License and Decommissioning Costs (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Dec. 31, 2017	Mar. 31, 2016	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2016	Sep. 30, 2016
Contract revenue current work					$ 30.4
Contract revenue past work					8.1
D&D Expense	$ 5.9	$ (7.0)			$ (19.0)
Decontamination and decommissioning obligations - total	$ 1.0
2018 ORNL Contract [Member] | Scenario, Forecast [Member]
Contract value			$ 16.0
2017 ORNL Contract [Member]
Contract value				$ 25.0
Contract monthly revenue				2.0
Contract milestone payments				$ 1.0
2016 ORNL Contract [Member]
Contract monthly revenue						$ 2.7