Summary of Accounting Policies - Narrative (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Jan. 01, 2021	Dec. 31, 2020
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accumulated deficit	$ (345,162)	$ (262,551)	$ (270,313)
1.75% Convertible Senior Notes due 2023
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Debt conversion	$ 226
Revision of Prior Period, Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accumulated deficit		$ 7,762