Research Funding (Details) - USD ($) $ in Millions	1 Months Ended		3 Months Ended
	Mar. 31, 2018	May 31, 2017	Mar. 31, 2019	Mar. 31, 2018	Feb. 28, 2017
Deferred Revenue Arrangement [Line Items]
Grants awarded	$ 8.6			$ 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			0.6	$ 0.6
Accrued Liabilities [Member]
Deferred Revenue Arrangement [Line Items]
Accrued grant funding			2.6
Other Long-Term Liabilities [Member]
Deferred Revenue Arrangement [Line Items]
Accrued grant funding			$ 0.9