Organization - Narrative (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2020 USD ($) segment product	Mar. 31, 2019 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Number of therapy products | product	2
Number of reportable segments | segment	1
Accumulated deficit	$ 383,384		$ 378,679
Net loss	4,705	$ 2,844
Cash, cash equivalents, and restricted cash	45,712	$ 35,084	26,978	$ 18,286
Cash and cash equivalents	45,623		$ 26,889
Short term investments	$ 37,700