License Agreement - Narrative (Details) - USD ($) $ in Thousands		3 Months Ended
	Dec. 19, 2019	Mar. 31, 2020	Mar. 31, 2019
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Acquired in-process research and development		$ 202,250	$ 56,000
Pharma Mar, S.A.
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Tiered royalty fees percentage, maximum	30.00%
Upfront Payments | Pharma Mar, S.A.
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Acquired in-process research and development		$ 200,000
Accelerated And/Or Full Regulatory Approval Milestone Payments | Pharma Mar, S.A.
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Research and development expense, not yet incurred	$ 250,000
Commercial Milestone Payments | Pharma Mar, S.A.
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Research and development expense, not yet incurred	$ 550,000