Fair Value of Financial Assets and Liabilities - Measured on a Recurring Basis (Details) - Fair Value, Recurring - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Cash equivalents—money market funds	$ 44,834	$ 63,637
Fair value of derivative liability	455
Embedded derivative liability		18
Embedded derivative liability
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Embedded derivative liability		18
Level 1
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Cash equivalents—money market funds	16,816	23,638
Fair value of derivative liability	0
Embedded derivative liability		0
Level 1 | Embedded derivative liability
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Embedded derivative liability		0
Level 2
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Cash equivalents—money market funds	28,018	39,999
Fair value of derivative liability	0
Embedded derivative liability		0
Level 2 | Embedded derivative liability
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Embedded derivative liability		0
Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Cash equivalents—money market funds	0	0
Fair value of derivative liability	$ 455
Embedded derivative liability		18
Level 3 | Embedded derivative liability
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Embedded derivative liability		$ 18