Summary of Significant Accounting Policies - Revenue Recognition (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Jan. 01, 2018
Revenue Recognition
Accumulated deficit	$ (1,073,096)	$ (1,013,316)
Deferred revenue	3,386	254
Accounts receivable	$ 1,802	$ 1,015
ASC 606
Revenue Recognition
Accumulated deficit			$ (1,300)
Deferred revenue			(800)
Accounts receivable			$ 500