Intangible Assets - Schedule of Finite-Lived Intangible Assets (Details) - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2017	Mar. 31, 2018
Finite-Lived Intangible Assets [Line Items]
Cost	$ 14.4	$ 14.4	$ 10.1
Accumulated amortization	(3.5)	(3.5)	(2.4)
Impairment charges	(2.7)	(2.7)
Intangible assets, net	8.2	8.2	7.7
Capacity Agreement
Finite-Lived Intangible Assets [Line Items]
Cost	10.1	10.1	10.1
Accumulated amortization	(1.9)	(1.9)	(2.4)
Impairment charges		0.0
Intangible assets, net	8.2	8.2	7.7
Developed Technology
Finite-Lived Intangible Assets [Line Items]
Cost	4.3	4.3	0.0
Accumulated amortization	(1.6)	(1.6)	0.0
Impairment charges		(2.7)
Intangible assets, net	$ 0.0	$ 0.0	$ 0.0