Research Funding (Details) - USD ($) $ in Millions	1 Months Ended		3 Months Ended		6 Months Ended
	Mar. 31, 2018	May 31, 2017	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Feb. 28, 2017
Deferred Revenue Arrangement [Line Items]
Grants awarded	$ 8.6						$ 12.2
Funding of grant award		$ 5.7
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			$ 0.7	$ 0.6	1.3	$ 1.3
Accrued Liabilities [Member]
Deferred Revenue Arrangement [Line Items]
Accrued grant funding			2.7		2.7
Other Long-Term Liabilities [Member]
Deferred Revenue Arrangement [Line Items]
Accrued grant funding			$ 0.2		$ 0.2