Research Funding (Details) - USD ($) $ in Millions	1 Months Ended			3 Months Ended		9 Months Ended		20 Months Ended
	Mar. 31, 2018	Dec. 31, 2017	May 31, 2017	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Feb. 28, 2017
Deferred Revenue Arrangement [Line Items]
Grants awarded	$ 8.6								$ 12.2
Funding of grant award			$ 5.7					$ 7.9
Milestone payment received on grant award		$ 1.9
Progress payment received on grant award	$ 0.3
Research and Development [Member]
Deferred Revenue Arrangement [Line Items]
Amortization of accrued grant funding to offset expense				$ 0.6	$ 0.4	$ 1.9	$ 0.7
Accrued Liabilities [Member]
Deferred Revenue Arrangement [Line Items]
Accrued grant funding				2.6		2.6		2.6
Other Long-Term Liabilities [Member]
Deferred Revenue Arrangement [Line Items]
Accrued grant funding				$ 2.2		$ 2.2		$ 2.2