Intangible Assets - Narrative (Details) € in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2019 EUR (€)	Sep. 30, 2018 USD ($)
Finite-Lived Intangible Assets [Line Items]
Amortization expense	$ 0.2	$ 0.2	$ 0.6		$ 0.6
Estimated future amortization expense for intangible assets, remainder of year	0.2		0.2
Estimated future amortization expense for intangible assets, per year thereafter	$ 0.8		$ 0.8
Remaining amortization period			8 years 6 months	8 years 6 months
Collaborative Arrangement
Finite-Lived Intangible Assets [Line Items]
Milestone payments that triggered intangible asset recognition			$ 8.7	€ 8.0