Organization - Narrative (Details) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2021 USD ($) product	Jun. 30, 2021 USD ($)	Mar. 31, 2021 USD ($)	Sep. 30, 2020 USD ($)	Jun. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Sep. 30, 2021 USD ($) product segment	Sep. 30, 2020 USD ($)	Aug. 27, 2021 USD ($)	Dec. 31, 2020 USD ($)
Subsidiary, Sale of Stock [Line Items]
Number of therapy products | product	2						2
Number of reportable segments | segment							1
Accumulated deficit	$ 387,821						$ 387,821			$ 375,815
Net loss	4,931	$ 3,786	$ 3,289	$ (3,618)	$ 8,269	$ 4,705	12,006	$ 9,356
Cash and cash equivalents	54,553			$ 43,507			54,553	$ 43,507		$ 33,620
Short term investments	$ 64,000						$ 64,000
At-The-Market
Subsidiary, Sale of Stock [Line Items]
Aggregate sale proceeds of up to									$ 200,000