License, Collaboration, and Funding Agreements - Research and Development Incentive Program (Details) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Other income		$ 517	$ 0	$ 0
Research and Development Incentive Program
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Amount due under incentive receivable plan		2,000
Other income		$ 446
MTS Austria
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Reimbursement rate for research and development		0.14
Subsequent Event | Research and Development Incentive Program
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Other income	$ 1,500