Basis of Presentation - Financial Statement Impact (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Jan. 01, 2018	Dec. 31, 2017
Adoption of ASC 606 as of January 1, 2018	$ 0.1
Unbilled contract revenue			$ 0.1
Accumulated deficit	(309.4)		(284.4)	$ (284.5)
Revenue, Contract Services	(14.4)	$ (6.4)
Net income (loss)	(25.0)	7.6
Advances from customers	0.3
Cost of sales - separative work units and uranium	34.8	2.7
Nonoperating components of periodic benefit expense (income), net	(1.6)	(0.4)
Net cash used in operating activities	(52.3)	(73.0)
Net cash used in financing activities	(3.0)	(36.6)
Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
Unbilled contract revenue			0.1
Accumulated deficit			$ 0.1
Revenue, Contract Services	(0.4)
Net income (loss)	(0.4)
Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Revenue, Contract Services	(14.8)
Net income (loss)	$ (24.6)
Scenario, Previously Reported [Member]
Cost of sales - separative work units and uranium		2.3
Net cash used in operating activities		(82.0)
Net cash used in financing activities		(27.6)
Restatement Adjustment [Member]
Cost of sales - separative work units and uranium		0.4
Nonoperating components of periodic benefit expense (income), net		0.4
Net cash used in operating activities		9.0
Net cash used in financing activities		$ (9.0)