Research Funding (Details) - USD ($) $ in Millions	1 Months Ended			3 Months Ended
	Mar. 31, 2018	Dec. 31, 2017	Oct. 31, 2017	Mar. 31, 2018	May 31, 2017	Feb. 28, 2017
Deferred Revenue Arrangement [Line Items]
Grants receivable	$ 8.6			$ 8.6		$ 12.2
Grants receivable, current					$ 5.7
Revenue from grants	0.3	$ 1.9	$ 1.9	7.9
Research and Development [Member]
Deferred Revenue Arrangement [Line Items]
Amortization of deferred credit				0.6
Accrued Liabilities [Member]
Deferred Revenue Arrangement [Line Items]
Deferred grant revenue	2.6			2.6
Other Long-Term Liabilities [Member]
Deferred Revenue Arrangement [Line Items]
Deferred grant revenue	$ 3.4			$ 3.4